Who knows ninety-one?
Please cite/link your sources, if possible. At some point in the next few days, I will:
Upvote all interesting answers.
Accept the best answer.
Go on to the next number.
I wouldn't normally do gematrias, but this has a double 91ness:
91 is the gematria of sukkah (malei) as well as the perek number in tehillim which expresses trust in Hashem's protection.
YDK's answer reminded me of another double gematria:
אמן = the names הוי-ה and א-דני, equaling 91.
[Baal Haturim (to Deut. 27:26) comments that this is why "one who answers Amen is greater than the one who recited the blessing" (Berachos 53b), because his Amen encapsulates two Divine names.]
Eruvin 56a cites Shmuel's statement that the interval between the beginning of one season and the next is 91 days (plus 7.5 hours). This is based on dividing a solar year of [nominally] 365.25 days into 4 parts. (Rashi)
91 are the total number of parshiyos (open and closed sections) in Chumash Bereishis - the least of any of the five chumashim, even though it's the longest of them.
There are 91 leap years in a cycle of 247 years.
Yaakov was 91 at Yosef's birth.