There has been at least one request for me to provide more comprehensive information regarding my claim that the Ibn Ezra says various Pentateuchal verses were not written by Moses (as dictated by God). Here you go:
As I quote in "Rabbinic vs. Modern Academic Beliefs", Ibn Ezra says the following in his comment on Deuteronomy 34:1, the twelfth-last verse of Deuteronomy:
ויעל משה. לפי דעתי, כי מזה הפסוק כתב יהושע, כי אחר שעלה משה לא כתב. ובדרך נבואה כתבו; והעד, ויראהו ה', גם ויאמר ה' אליו, גם ויקבור׃
"'And Moses ascended.' My view is that Joshua wrote [the final verses of Deuteronomy] beginning with this verse, for Moses did not write after he ascended. He [Joshua] wrote it prophetically, as indicated by [statements of facts he could not otherwise have known, such as] 'God showed him...', 'God said to him...', '[God] buried...'."
The Talmud (Bava Batra 15a) records a dispute regarding the final eight verses of Deuteronomy.
תניא, "וימת שם משה עבד ה'." אפשר משה מת [/חי] וכתב "וימת שם משה?" אלא עד כאן כתב משה; מכאן ואילך כתב יהושע -- דברי רבי יהודה, ואמרי לה רבי נחמיה. אמר לו רבי שמעון, אפשר ספר תורה חסר אות אחת וכתיב "לקוח את ספר התורה הזה?" אלא עד כאן הקדוש ברוך הוא אומר ומשה אומר וכותב; מכאן ואילך הקדוש ברוך הוא אומר ומשה כותב בדמע׃
It was taught in a baraita: "'Moses, the servant of God, died there.' Is it possible that Moses was dead [alt.: was alive] and wrote 'Moses died there?' Rather, Moses wrote until this point [in Deuteronomy]; Joshua wrote from this point onward" -- the words of Rabbi Yehudah, or, according to some, Rabbi Nehemiah. Rabbi Shimon said to him, "Is it possible that the book of the law [the Pentateuch] was missing even one letter and yet it was written [that God said to Moses], 'Take this book of the law?' Rather, until this point God dictated and Moses repeated orally and wrote down; from this point onward God dictated and Moses wrote down with tears."
[Note: There is more than one opinion regarding the meaning of the word בדמע in this passage. I have selected a common interpretation, "with tears." I do not believe that the differences in interpretation are relevant to this discussion.]
Ibn Ezra's view, cited above, that the last 12 verses of Deuteronomy were written by Joshua clearly contradicts both of these tannaic opinions. The first opinion, that of Rabbi Yehudah or Rabbi Nehemiah, states specifically that "Moses wrote until this point" [the eighth-last verse of Deuteronomy]; the second, that of Rabbi Shimon, insists that every letter of the Torah was written by Moses.
In the middle of his comment (s.v. "מחרב") on Deuteronomy 1:2, Ibn Ezra makes the following enigmatic statement:
ואם תבין סוד השנים עשר, גם "ויכתוב משה," "והכנעני אז בארץ," "בהר ה' יראה," גם "הנה ערשו ערש ברזל," תכיר האמת׃
And if you understand the secret of the twelve, also "Moses wrote" (Deuteronomy 31:22), "and the Canaanite[s] were then in the land" (Genesis 12:6), "on God's mountain, he will be seen" (Genesis 22:14), also "Behold, his bed was made of iron" (Deuteronomy 3:11), you will recognize the truth.
I believe that "the twelve" are the final twelve verses of the Pentateuch, which, as we have seen, Ibn Ezra explicitly states were not written by Moses. The "secret of the twelve" is a reference to non-Mosaic authorship. In this most recently quoted passage, Ibn Ezra claims that the introduction to the book of Deuteronomy, as well as the other verses or verse segments he lists, were not written by Moses. (Whether they were written by Joshua, or by someone else, he does not say.)
I find it fairly easy to understand why Ibn Ezra would make such claims about the specific verses he cites, with the sole exception of (ironically) the first verses of Deuteronomy. I will now proceed to quote each verse, explain what might have motivated Ibn Ezra to question Moses's authorship of it, cite any comments Ibn Ezra makes on each verse ad locum, and compare those comments to his statement at Deuteronomy 1:2.
Deuteronomy 31:22 reads,
ויכתב משה את השירה הזאת ביום ההוא וילמדה את בני ישראל׃
Moses wrote this song on that day, and he taught it to the children of Israel.
Now, Moses died very shortly thereafter. If he wrote this verse, it would have sounded very peculiar, because "on that day" (ביום ההוא) generally carries the connotation of more than a short time before. It would have been far better phraseology if employed significantly after the event, and therefore after Moses's death.
Ibn Ezra on Deuteronomy 31:22 itself says,
ביום ההוא. שלא איחר הדבר. ויתכן שהיה יום מותו אחר מכתב דברי התורה, כי השירה כתב משה עמה׃
"On that day." [Meaning] that he did not delay the matter. And it could be that the day of his death was after the writing of the words of the Torah, for the song itself Moses wrote with it.
Ibn Ezra states that "on that day" signifies that Moses did not delay in performing the task he had been assigned. If that is what it means, then there is no peculiarity in the phrase to justify the argument I presented in the previous paragraph. Note in the following paragraphs (see, for example, the bracketed discussion of Ibn Ezra's commentary to Genesis 12:6), however, that Ibn Ezra does not always seem absolute in his conviction that the verses he listed at Deuteronomy 1:2 actually carry the "secret" to which he refers several times, and that he sometimes advances other possible interpretations of the verses, according to which their Mosaic authorship is more plausible. Thus at 1:2 he may be presenting the option that the awkward wording of 31:22 suggests non-Mosaic authorship, whereas at 31:22 itself, he proposes another interpretation of the wording, one that is compatible with Moses having written it.
It is worth pointing out that Ibn Ezra clearly felt that there was something fishy about the "on that day" of 31:22; otherwise he need not have commented on it.
Genesis 12:6 reads,
ויעבר אברם בארץ עד מקום שכם עד אלון מורה והכנעני אז בארץ׃
Abram passed through the land until the place of Shechem, until the plain of Moreh; and the Canaanite[s] were then in the land.
It is difficult to understand why Moses would have written "the Canaanites were then in the land," implying that by Moses's time they were not, when in fact they continued to be there until years after his death. Again, such a statement would more logically come from a later author, one living after the Israelite conquest of Canaan, during which the Canaanite population of the land, if not eliminated, was certainly sharply reduced, both in number and in power.
Ibn Ezra on Genesis 12:6, s.v. והכנעני אז בארץ, says,
יתכן שארץ כנען תפשה כנען מיד אחר. ואם איננו כן יש לו סוד, והמשכיל ידום׃
It could be that Canaan took the land of Canaan immediately after [the preceding events in the verse]. If it is not so, then [the verse] has a secret, and he who is intelligent shall be silent.
So here, as mentioned earlier, Ibn Ezra appears to be allowing for two possibilities: one that reconciles the problematic last three words with Mosaic authorship, and one that concedes that the verse (at least the end of it) was written later and by someone else.
Genesis 22:14 states,
ויקרא אברהם שם המקום ההוא ה' יראה אשר יאמר היום בהר ה' יראה׃
Abraham called the name of that place "God will see;" today, it is therefore said, "On God's mountain, he will be seen" (translation after the semi-colon from Rabbi Aryeh Kaplan's The Living Torah).
Neither Moses nor, likely, almost any Israelite for at least two centuries prior to Moses's death had even seen this mountain, and it is unlikely that Moses could have truthfully stated, "Today, it is therefore said, 'On God's mountain, he will be seen.'" More likely almost nothing was ever said about it. Again, it would be a much more sensible thing to say for a person who lived in the land of Israel after the Israelite conquest and settlement, something Moses did not do.
Ibn Ezra's comment on Genesis 22:14 is a pithy
וטעם "בהר ה' יראה" ב"אלה הדברים"׃
The explanation of "on God's mountain, he will be seen" is in "These are the words" [i.e., his commentary on the first verses of Deuteronomy].
Here, Ibn Ezra simply refers the reader to his comments at the beginning of Deuteronomy, cited above.
Deuteronomy 3:11 reads,
כי רק עוג מלך הבשן נשאר מיתר הרפאים הנה ערשו ערש ברזל הלה הוא ברבת בני עמון תשע אמות ארכה וארבע אמות רחבה באמת איש׃
For only Og, King of Bashan, remained from the last of the Rephaim. His bed was made of iron, and is in the Ammonite city of Rabbah: its length is nine cubits, and its width is four cubits, the cubit being that of a normal man (translation adapted from Kaplan).
Why would Moses need to tell the people about Og's bed? They had fought him within the year! They had either seen him themselves, or heard about him from others. It would appear to have been totally superfluous for Moses to make such a statement. However, someone living in a later generation, one that had never seen Og for themselves, might be quite impressed indeed if told that they could personally view Og's massive bed, which survived until that day, made as it was of iron, in the city of Rabbah.
Ibn Ezra makes no comment ad locum on the verse.
There is one more comment of Ibn Ezra I'd like to cite, although its content is slightly further afield. At Deuteronomy 34:6, he writes:
עד היום הזה. דברי יהושע. ויתכן שכתב זה באחרית ימיו׃
"[No man] until this day [knows the site of Moses's burial]". [These are] the words of Joshua. And it is plausible that he wrote this at the end of his life.
I hope I've explained things clearly. If anyone can advance an alternative set of explanations of the various passages that I have quoted from Ibn Ezra's commentary, feel free to publish it (in the comments, or a separate post, etc). I'm not wedded to the idea that Ibn Ezra believed in, or at least considered possible, the non-Mosaic authorship of some parts of the Torah, but at this point, I don't know how else to understand what he wrote.
Once again, I'd like to thank Dr. Moshe Bernstein of Yeshiva University for much of the information I've provided here.