מדרש על דברים 14:28

(Devarim 14:28) "(If one delayed giving his tithes of the first and second years) From the end of three years, you shall remove all the tithe of your produce": I might think, even on the festival; it is, therefore, written (Ibid. 26:12) "When you finish tithing" (and the tithing of the third year's produce is not completed until Channukah of the fourth year).