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: 5951
Abu Huraira reported Allah's Messenger (may peace be upon him) as saying to Hasan: O Allah, behold, I love him. Thou too love him and love one who loves him.