From Sahih Bukhari (Hadith 6003):
Narrated Usama bin Zaid:Allah's Messenger (ﷺ) 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
Reference: Bukhari 6003