Hadithcore
Hadith #2104660

And in another narration of al-Bukhari and Muslim, ['Aishah (RA)] narrated:

"He used to pray ten Rak'at (of prayer), and making it Witr by one Rak'at, and he used to pray the two (Sunnah) Rak'at of Fajr, so that it became thirteen Rak'at."

وَفِي رِوَايَةٍ لَهُمَا عَنْهَا: { كَانَ يُصَلِّي مِنْ اَللَّيْلِ عَشْرَ رَكَعَاتٍ, وَيُوتِرُ بِسَجْدَةٍ, وَيَرْكَعُ رَكْعَتَيْ اَلْفَجْرِ, فَتِلْكَ ثَلَاثُ عَشْرَةَ } [1]‏ .‏

References2 variants
Sunnah.com reference
Book 2, Hadith 282
Arabic/English book reference
Book 2, Hadith 373