A.T. Robertson Commentary Mark 12:19

"Teacher, Moses wrote unto us, If a man`s brother die, and leave a wife behind him, and leave no child, that his brother should take his wife, and raise up seed unto his brother." — Mark 12:19 (ASV)

Moses wrote (Μωυσης εγραψεν). So Lu 20:28 (Genesis 38:8; De. 25:5f.). Matthew has "said" (ειπεν).