Musannaf Ibn Abi Shayba 3:5834

Hafs narrated to us, from ‘Asim, from ‘Ikrimah, from Ibn ‘Abbas, that the Prophet (peace and blessings of Allah be upon him) stayed for seventeen [days] shortening the prayer. He said: And Ibn ‘Abbas said: Whoever stays for seventeen [days] shortens the prayer, and whoever stays more than that completes it.