At three periods of the year they withdraw [funds] from the [treasury] chamber; fifteen days before Pesach, fifteen days be-fore Shavuos, and fifteen days before Succos. And these are also the designated dates for the animal tithe —- [these are] the words of R’ Akiva.  Ben Azzai says: [The three periods are] on the twenty-ninth of Adar, on the first of Sivan, and on the twenty-ninth of Av.  R’ Elazar and R’ Shimon says: [The three periods are] on the first of Nissan, on the first of Sivan, and on the twenty-ninth of Elul. Why did they say “on the twenty-ninth [of Elul]” instead of saying “on the first of Tishrei”? —- because that [day] is a festival, and one may not tithe on a festival, therefore they advanced it to the twenty-ninth of Elul.