Yahya bin al-Jazzar (may Allah have mercy on him) said: Some of the Companions of the Prophet (peace and blessings be upon him) came to Sayyidah Umm Salamah (may Allah be pleased with her) and said: "O Mother of the Believers, narrate to us something about the Messenger of Allah (peace and blessings be upon him)." She said: "His outward and his inward (his open and his hidden state) were the same." Then Sayyidah Umm Salamah (may Allah be pleased with her) felt regret and said: "I have disclosed the secret of the Messenger of Allah (peace and blessings be upon him)." So when he (peace and blessings be upon him) came in, I told him (peace and blessings be upon him), and he (peace and blessings be upon him) said: "You did well."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 20044
It is narrated from Sayyidah Umm Salamah (may Allah be pleased with her) that the Messenger of Allah (peace and blessings be upon him) used to pray witr with thirteen rak'ahs; then, when he (peace and blessings be upon him) grew older and weaker, he began to pray witr with seven rak'ahs.
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 20045