Sahih Muslim 2924 a
The Book of Tribulations and Portents of the Last Hour
Ibn Sayyad
'Abdullah reported: We were along with Allah's Messenger (ﷺ) that we happened to pass by children amongst whom there was Ibn Sayyad. The children made their way but Ibn Sayyad kept sitting there (and it seemed) as if Allah's Messenger (ﷺ) did not like it (his sitting with the children) and said to him: May your nose he besmeared with dust, don't you bear testimony to the fact that I am the Messenger of Allah? Thereupon he said: No, but you should bear testimony that I am the messenger of Allah. Thereupon 'Umar b. Khattab said: Allah's Messenger (ﷺ) , permit me that I should kill him. Thereupon Allah's Messenger (ﷺ) said: If he is that person who is in your mind (Dajjal ), you will not be able to kill him.