Sahih Muslim
The Book Pertaining to the Merits of the Companions (Allah Be Pleased With Them) of the Holy Prophet (May Peace Be Upon Him) (Kitab Al-Fadail Al-Sahabah)
Book Number: 031 / Hadith Number: 5952
Al-Bara' b. Azib reported: I saw Hasan b. 'Ali upon the shoulders of Allah's Apostle (may peace be upon him) and he was saying: O Allah, I love him, and love him Thou.