Musannaf Ibn Abi Shayba 9:794

Waki’ narrated to us, from Musa ibn ‘Ubaydah, he said: Nafi’ ibn Jubayr ibn Mut’im narrated to me, from a man among the companions of the Prophet, may Allah bless him and grant him peace, who said: "If he lets down a curtain or closes a door, then the dowry has become obligatory."