מדרש על ראש השנה 7:1

"on the festival of matzoth, and on the festival of Shavuoth, and on the festival of Succoth": Because it is written (Ibid. 12:5) "and you shall come there (6) and you shall bring there your sacrifices, etc.," I might think (that if he fails to do so) on the first festival he is in transgression of (Ibid. 23:33) "You shall not delay to pay it"; it is, therefore, written (Bamidbar 29:39) "These shall you offer to the L-rd on your festivals." I might think (that he is in transgression if he does not offer them on the first) two festivals; it is, therefore, written "on the festival of matzoth, and on the festival of Shavuoth, and on the festival of Succoth." We are hereby taught that he is not in transgression until all the festivals of the year have passed. R. Shimon says: Three festivals in order, and Succoth last. R. Elazar b. Shimon says: It need not be written "the festival of Succoth," for that is the subject of the verse. Why is it written? To indicate that it (i.e., passing it) is the cause (of the transgression).