Musannaf Ibn Abi Shayba 9:792

Ibn ‘Ulayyah narrated to us, from ‘Awn, from Zurarah ibn Awfa, who said: I heard him saying: The rightly-guided, rightly-directed Caliphs decreed that whoever closes a door or lets down a curtain, the dowry (mahr) has become obligatory, and the waiting period (‘iddah) has become obligatory.