We were along with Messenger of Allah 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 Messenger of Allah 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: Messenger of Allah, permit me that I should kill him. Thereupon Messenger of Allah ﷺ said: If he is that person who is in your mind (Dajjal ), you will not be able to kill him.  

كُنَّا مَعَ رَسُولِ اللَّهِ ﷺ فَمَرَرْنَا بِصِبْيَانٍ فِيهِمُ ابْنُ صَيَّادٍ فَفَرَّ الصِّبْيَانُ وَجَلَسَ ابْنُ صَيَّادٍ فَكَأَنَّ رَسُولَ اللَّهِ ﷺ كَرِهَ ذَلِكَ فَقَالَ لَهُ النَّبِيُّ ﷺ تَرِبَتْ يَدَاكَ أَتَشْهَدُ أَنِّي رَسُولُ اللَّهِ فَقَالَ لاَ بَلْ تَشْهَدُ أَنِّي رَسُولُ اللَّهِ فَقَالَ عُمَرُ بْنُ الْخَطَّابِ ذَرْنِي يَا رَسُولَ اللَّهِ حَتَّى أَقْتُلَهُ فَقَالَ رَسُولُ اللَّهِ ﷺ إِنْ يَكُنِ الَّذِي تَرَى فَلَنْ تَسْتَطِيعَ قَتْلَهُ