Musnad Abu Ya'la al-Mawsili 153:98

Suwayd ibn Sa'id narrated to us, Mu'tamir narrated to us, from Burayd ibn Sinan, from al-Zuhri, from Salim, from his father, who said: The Messenger of Allah (peace be upon him) said: "It is not appropriate for anyone to spend three nights except that his will is with him." He (Salim) said: So I have not spent a night except that my will is placed with me, or as he said.