Imam al-Hasan al-Basri (may Allah have mercy on him) narrates from his mother, and she from the Mother of the Believers, Sayyidah Umm Salamah (may Allah be pleased with her), that "The Prophet (peace and blessings be upon him) used to pray two rak'ahs sitting after his witr."
No one other than Zakariyya bin Hakim and Maymun bin Musa al-Mara'i narrated this hadith from Imam al-Hasan al-Basri (may Allah have mercy on him).
Hadith Referenceالمعجم الأوسط / باب الميم / 7094
Hadith Takhrij«أخرجه الترمذي فى «جامعه» برقم: 471، وابن ماجه فى «سننه» برقم: 1195، والبيهقي فى «السنن الكبرى» برقم: 4899، والدارقطني فى «سننه» برقم: 1682، وأحمد فى «مسنده» برقم: 27196، والطبراني فى «الكبير» برقم: 859، 860»