Musnad Ahmad 1156:108

Mu'awiyah ibn 'Amr narrated to us, Ibrahim ibn Sa'd narrated to us, he said: Muhammad ibn Ishaq narrated to me, from Muhammad ibn 'Abd al-Rahman ibn Husayn, from 'Awf ibn al-Harith, from Umm Salamah, she said: The Messenger of Allah, peace and blessings of Allah be upon him, said to his wives: "Indeed, the one who will be compassionate toward you after me is the truthful, the righteous." O Allah, give 'Abd al-Rahman ibn 'Awf to drink from the Salsabil of Paradise.