It is related that Abu Hurayra said, "I never sae al-Hasan withoutmy eyes overflowing with tears. That is because the Prophet, may Allahbless him and grant him peace, went out one day and I found him in themosque. He took my hand and I went along with him. He did not speak tome until we reached the market of Banu Qaynuqa'. He walked around it andlooked. Then he left and I left with him until we reached the mosque. Hesat down and wrapped himself in his garment. Then he said, 'Where is thelittle one? Call the little one to me.' Hasan came running and jumped intohis lap. Then he put his hand in his beard. Then the Prophet, may Allahbless him and grant him peace, opened his mouth and put his tongue in hismouth. Then he said, O Allah, I love him, so love him and the one who loveshim!'"
English reference: Book 48, Hadith 1183
Arabic reference: Book 1, Hadith 1183