Musnad Ahmad 1156:88

Yunus narrated to us, Ibrahim—meaning Ibn Sa'd—narrated to us, from Muhammad ibn Ishaq, from Muhammad ibn 'Abd al-Rahman ibn 'Abd Allah ibn al-Husayn, from 'Awf ibn al-Harith, from Umm Salamah, who said: I heard the Messenger of Allah, peace and blessings of Allah be upon him, saying to his wives: "Indeed, the one who will be compassionate toward you after me is truly the truthful, the righteous one. O Allah, give 'Abd al-Rahman ibn 'Awf to drink from the Salsabil of Paradise."