Musnad Ahmad 850:5

'Abdullah narrated to us, saying: "I found in my father's book in his own handwriting, and I am most certain that I heard it from him." 'Ali ibn 'Abdullah narrated to us, Nasiḥ ibn al-'Ala' Abu al-'Ala', the freed slave of Banu Hashim, narrated to us, 'Ammar ibn Abi 'Ammar, the freed slave of Banu Hashim, narrated to us, that he passed by 'Abd al-Rahman ibn Samurah while he was at the river of Umm 'Abdullah, where the water was flowing, with his young servants and his freed slaves. 'Ammar said to him: "O Abu Sa'id, the Friday [prayer]." 'Abd al-Rahman ibn Samurah said to him: "Indeed, the Messenger of Allah, peace and blessings of Allah be upon him, used to say: 'If it is a day of heavy rain, let one of you pray in his dwelling.'"