Midrasch zu Bereschit 34:12

"mahor yimharenah to himself as a wife": What is the intent of this? From (Devarim 22:29) "then the man who lay with her shall give," I might think that just as when he ravishes her he gives (knass) immediately, so, when he entices her. We are, therefore, apprised that he (the father) imposes it (the fine) upon him as mohar," "mohar" being a kethubah, as in (Genesis 34:12) "Impose upon me much mohar and dower, and I will give it as you tell me, but give me the maiden as a wife."