From when do we mention the powers of rain? R' Eliezer says: From the first Yom Tov of the festival. R' Yehoshua says: From the last Yom Tov of the festival.  R' Yehoshua said to him: Since rain is but a symptom of curse during the festival, why mention [it]?  R' Eliezer replied to him: I, too, did not say to re-quest [rain], but [merely] to mention “He causes the wind to blow and the rain to fall,” in its proper season.  He responded: If so, one should always mention [the powers of rain]!