וְהָיָה כִּי-תִמְצֶאןָ אֹתוֹ רָעוֹת רַבּוֹת, וְצָרוֹת,
וְעָנְתָה הַשִּׁירָה הַזֹּאת לְפָנָיו לְעֵד, כִּי לֹא תִשָּׁכַח מִפִּי
For it shall not be forgotten out of the mouths of their seed: He promised them that the Torah will not be removed from them nor will it disappear. There is a tradition that the Jews did not have the Torah during the First Exile. Ezra Hasofer wrote down from memory all the 24 books and could not remember the first part of this sentence in Shir Hashirim -
יב לֹא יָדַעְתִּי--נַפְשִׁי שָׂמַתְנִי, מַרְכְּבוֹת עַמִּי נָדִיב.
12 Before I was aware, my soul set me upon the chariots of my princely people. (Shir Hashirim 6:12)
He asked an Am Ha’aretz (an unlearned man) if he remembered the beginning of the verse in Shir Hashirim that ends with מַרְכְּבוֹת עַמִּי נָדִיב. To which the man said
לֹא יָדַעְתִּי-- - I don’t know! That jolted Ezra’s memory and he remembered the missing words. The Midrash continues that this is why the Mesora has עה on this verse, the acronym for Am Ha’aretz, to remind us that Ezra needed the help of one.
I have very little to say about this Midrash other than that it triggers a great many thoughts about how some of our rabbis understood Ezra’s role in writing down the torah. The fact that it was an accepted traditional story in the Jewish community in Yemen is even more telling.
 For a short overview of the Yemmenite Midrashim, see Torah Shleima Vol. 1 in the introduction note 11.