Musannaf Ibn Abi Shayba 9:1074

Ibn ‘Ulayyah narrated to us, from Ibn Jurayj, who said: Mujahid said: “{The one in whose hand is the marriage knot} is the husband. {Unless they forgo} means the woman absolves her half. {Or he forgoes in whose hand is the marriage knot} means the husband completes the entire dowry.”