Musnad Abu Ya'la al-Mawsili 155:273

Zakariya ibn Yahya narrated to us, Hushaym narrated to us, from al-Zuhri, from Abu Salamah, from Abu Hurayrah, who said: Uyainah ibn Hisn al-Fazari entered upon the Messenger of Allah, may Allah bless him and grant him peace, and he saw him kissing al-Hasan or al-Husayn. He said: "O Messenger of Allah, I have had ten children born to me, and I have not kissed any one of them." The Messenger of Allah, may Allah bless him and grant him peace, said: "Whoever does not show mercy will not be shown mercy."