Authentic
graded by Al-Albani
Mishkat al-Masabih 1284
Narrator:Umm Salamah
وَعَنْ أُمُّ سَلَمَةَ رَضِيَ اللَّهُ عَنْهَا أَنَّ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «كَانَ يُصَلِّي بَعْدَ الْوِتْرِ رَكْعَتَيْنِ» رَوَاهُ التِّرْمِذِيُّ وَزَادَ ابْنُ مَاجَه: خفيفتين وَهُوَ جَالس
Umm Salama said the Prophet used to pray two rak'as after the witr. Tirmidhi transmitted it, and Ibn Majah added that they were short ones which he prayed while sitting.
Cited in Mishkat al-Masabih (No. 1284).