Musannaf Ibn Abi Shayba 37:422

Ubayd Allah ibn Musa narrated to us, he said: Shayban informed us, from al-A'mash, from Shaqiq, from Abdullah, who said: We were walking with the Messenger of Allah (may Allah bless him and grant him peace), and we passed by some boys who were playing. They dispersed when they saw the Prophet (may Allah bless him and grant him peace), but Ibn Sayyad sat still. It was as if that angered the Prophet (may Allah bless him and grant him peace), so he said to him: "What is the matter with you? May your hands be covered in dust! Do you bear witness that I am the Messenger of Allah?" He replied: "Do you bear witness that I am the Messenger of Allah?" Umar said: "O Messenger of Allah, let me kill this wicked one." He said: "Leave him, for if he is the one you fear, you will not be able to kill him."