Musannaf Ibn Abi Shayba 9:1589

Abu Bakr narrated to us, he said: Abd al-A’la narrated to us, he said: It was asked regarding a man who married a woman upon an immediate or deferred [dowry], and he consummated the marriage with her, then she claimed that he had not given her the immediate [portion]. He said: Sa’id narrated to us, from Qatadah, that he used to say: The way out for him regarding the immediate [portion] is that if she says, "There remains upon him such and such," his consummation with her absolves him of it.