Zurarah bin Awfa (may Allah have mercy on him) said: The Rightly Guided Caliphs (may Allah be pleased with them) used to say: When he has closed the door and let down the curtain, the dower (mahr) and the waiting period ('iddah) have become obligatory.
This is mursal; Zurarah did not meet them, and we have narrated it from Umar and Ali (may Allah be pleased with them both) with a connected chain.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصداق / 14484