Musnad Ahmad 941:0

It was narrated from Usamah ibn Zayd that the Messenger of Allah (ﷺ) used to take him and Al-Hasan, and he would say: "O Allah, I love them both, so love them." In another narration: He would place me on one of his thighs and place Al-Hasan ibn ‘Ali on his other thigh, then he would embrace us both and say: "O Allah, have mercy on them, for I am merciful toward them."