Midrash su I Re 4:7

(Devarim 1:3) "And it was, in the fortieth year, in the eleventh month, on the first of the month, that Moses spoke to the children of Israel": What does this ("in the eleventh month") come to teach us? If that a year has eleven months, is it not written (Esther 3:13) "on the thirteenth day of the twelfth month, the month of Adar"? And thus is it written (I Kings 4:7) "And Solomon had twelve commissioners over all of Israel … (Ibid. 19) and one commissioner over the land." For which month? The intercalated month, whereby we are taught that the year (itself) is twelve months. R. B'na'ah says: Now before Solomon did we not know that the year was twelve months? Is it not written (I Chronicles 1:27) "… month by month throughout all the months of the year … the twelfth (marshal), for the twelfth month, etc." — But it ("the eleventh month") comes to teach us that in thirty-six days (from the first of Shvat ["the eleventh month"] to the sixth of Adar) Moses explained the entire Torah, as it is written (Devarim 34:8) "And they mourned Moses thirty days" and (Joshua 1:11) "for in three more days you will be crossing this Jordan," and (Ibid. 4:19) "And the people ascended from the Jordan on the tenth of the first month (Nissan)." Subtract thirty-three days retroactively and it is found that Moses died on the seventh of Adar. (And whence is it derived that Moses was born on the seventh of Adar? From (Devarim 31:2) "And he said to them: I am one hundred and twenty years old this day." Let "this day" not be written. Why is it written? (To signify) this day (the full circuit of) my years and days have been completed — whence it is derived that the Holy One Blessed be He "sits" and fills out the years of the righteous from day to day and from month to month and from hour to hour, as it is written (Shemoth 23:26) (If you are righteous) "the number of your days shall I complete." — whence it is derived that in thirty-six days Moses explained the entire Torah.