Musnad Abu Ya'la al-Mawsili 152:104

From al-A‘mash, from Abu Wa’il, 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, among whom was Ibn Sayyad. The boys fled, but Ibn Sayyad sat still. It was as if the Messenger of Allah (may Allah bless him and grant him peace) disliked that. The Messenger of Allah (may Allah bless him and grant him peace) said to him, "May your hands be covered in dust! Do you bear witness that I am the Messenger of Allah?" He said, "No, rather, you bear witness that I am the Messenger of Allah." ‘Umar said, "O Messenger of Allah, will you permit me to kill him?" The Messenger of Allah (may Allah bless him and grant him peace) said, "If he is who you think he is, you will not be able to kill him."