Musannaf Ibn Abi Shayba 28:322

Hushaym narrated to us, he said: Al-Kalbi narrated to us, from Abu Salih, from Ibn Abbas, who said: When the marriage of Zaynab was revealed, Zayd ibn Harithah went until he asked for permission to enter upon Zaynab. He said: So Zaynab said, "What do I have to do with Zayd?" He said: So the Messenger of Allah, peace and blessings of Allah be upon him, sent to her. He said: So she gave him permission, and he gave her the glad tidings that Allah had married her to His Prophet, peace and blessings of Allah be upon him. He said: So she fell down prostrate in gratitude to Allah.