Musnad Abu Ya'la al-Mawsili 155:52

Zahmūyah narrated to us, Hushaym narrated to us, from al-Zuhrī, from Abū Salamah, from Abū Hurayrah, who said: ‘Uyaynah ibn Ḥiṣn al-Fazārī came to the Messenger of Allah (may Allah bless him and grant him peace) and saw him kissing al-Ḥasan and al-Ḥusayn. He said, “Do you kiss them, O Messenger of Allah? I have had ten children born to me, and I have not kissed a single one of them.” The Messenger of Allah (may Allah bless him and grant him peace) said, “He who does not show mercy will not be shown mercy.”