Sahih Bukhari
Good Manners and Form (Al-Adab)
Volume: 008 / Book Number: 073 / Hadith Number: 32
Narrated Usama bin Zaid:
Allah's Apostle used to put me on (one of) his thighs and put Al-Hasan bin 'Ali on his other thigh, and then embrace us and say, "O Allah! Please be Merciful to them, as I am merciful to them. "