It is narrated by Safwan b. Muhriz that Jundab b. 'Abdullah al-Bajali during the stormy days of Ibn Zubair sent a message to 'As'as b. Salama:

Gather some men of your family so that I should talk to them. He ('As'as) sent a messenger to them (to the members of his family). When they had assembled, Jundab came there with a yellow hooded cloak on him, He said: Talk what you were busy in talking. The talk went on by turns, till there came his (Jundab's) turn. He took off the hooded cloak from his head and said: I have come to you with no other intention but to narrate to you a hadith of your Messenger: Verily the Messenger of Allah (ﷺ) sent a squad of the Muslims to a tribe of the polytheists. Both the armies confronted one another. There was a man among the army of polytheists who (was so dashing that), whenever he intended to kill a man from among the Muslims, he killed him. Amongst the Muslims too was a man looking forward to (an opportunity of) his (the polytheist's) unmindfulness. He (the narrator) said: We talked that he was Usama b, Zaid. When he raised his sword, he (the soldier of the polytheists) uttered:" There is no god but Allah," but he (Usama b. Zaid) killed him. When the messenger of the glad tidings came to the Messenger (ﷺ) he asked him (about the events of the battle) and he informed him about the man (Usama) and what he had done He (the Prophet (ﷺ) of Allah) called for him and asked him why he had killed him. He (Usama) said: Messenger of Allah, he struck the Muslims and killed such and such of them. And he even named some of them. (He continued): I attacked him and when he saw the sword he said: There is no god but Allah. The Messenger of Allah (ﷺ) said: Did you kill him? He (Usama) replied in the affirmative. He (the Prophet) remarked: What would you do with:" There is no god but Allah," when he would come (before you) on the Day of Judgment? He (Usama) said: Messenger of Allah, beg pardon for me (from your Lord). He (the Prophet) said: What would you do with:" There is no god but Allah" when he would come (before you) on the Day of Judgment? He (the Prophet) added nothing to it but kept saying: What would you do with:" There is no god but Allah," when he would come (before you) on the Day of Judgment?

حَدَّثَنَا أَحْمَدُ بْنُ الْحَسَنِ بْنِ خِرَاشٍ، حَدَّثَنَا عَمْرُو بْنُ عَاصِمٍ، حَدَّثَنَا مُعْتَمِرٌ، قَالَ سَمِعْتُ أَبِي يُحَدِّثُ، أَنَّ خَالِدًا الأَثْبَجَ ابْنَ أَخِي، صَفْوَانَ بْنِ مُحْرِزٍ حَدَّثَ عَنْ صَفْوَانَ بْنِ مُحْرِزٍ، أَنَّهُ حَدَّثَ أَنَّ جُنْدَبَ بْنَ عَبْدِ اللَّهِ الْبَجَلِيَّ بَعَثَ إِلَى عَسْعَسِ بْنِ سَلاَمَةَ زَمَنَ فِتْنَةِ ابْنِ الزُّبَيْرِ فَقَالَ اجْمَعْ لِي نَفَرًا مِنْ إِخْوَانِكَ حَتَّى أُحَدِّثَهُمْ ‏.‏ فَبَعَثَ رَسُولاً إِلَيْهِمْ فَلَمَّا اجْتَمَعُوا جَاءَ جُنْدَبٌ وَعَلَيْهِ بُرْنُسٌ أَصْفَرُ فَقَالَ تَحَدَّثُوا بِمَا كُنْتُمْ تَحَدَّثُونَ بِهِ ‏.‏ حَتَّى دَارَ الْحَدِيثُ فَلَمَّا دَارَ الْحَدِيثُ إِلَيْهِ حَسَرَ الْبُرْنُسَ عَنْ رَأْسِهِ فَقَالَ إِنِّي أَتَيْتُكُمْ وَلاَ أُرِيدُ أَنْ أُخْبِرَكُمْ عَنْ نَبِيِّكُمْ إِنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم بَعَثَ بَعْثًا مِنَ الْمُسْلِمِينَ إِلَى قَوْمٍ مِنَ الْمُشْرِكِينَ وَإِنَّهُمُ الْتَقَوْا فَكَانَ رَجُلٌ مِنَ الْمُشْرِكِينَ إِذَا شَاءَ أَنْ يَقْصِدَ إِلَى رَجُلٍ مِنَ الْمُسْلِمِينَ قَصَدَ لَهُ فَقَتَلَهُ وَإِنَّ رَجُلاً مِنَ الْمُسْلِمِينَ قَصَدَ غَفْلَتَهُ قَالَ وَكُنَّا نُحَدَّثُ أَنَّهُ أُسَامَةُ بْنُ زَيْدٍ فَلَمَّا رَفَعَ عَلَيْهِ السَّيْفَ قَالَ لاَ إِلَهَ إِلاَّ اللَّهُ ‏.‏ فَقَتَلَهُ فَجَاءَ الْبَشِيرُ إِلَى النَّبِيِّ صلى الله عليه وسلم فَسَأَلَهُ فَأَخْبَرَهُ حَتَّى أَخْبَرَهُ خَبَرَ الرَّجُلِ كَيْفَ صَنَعَ فَدَعَاهُ فَسَأَلَهُ فَقَالَ ‏"‏ لِمَ قَتَلْتَهُ ‏"‏ ‏.‏ قَالَ يَا رَسُولَ اللَّهَ أَوْجَعَ فِي الْمُسْلِمِينَ وَقَتَلَ فُلاَنًا وَفُلاَنًا - وَسَمَّى لَهُ نَفَرًا - وَإِنِّي حَمَلْتُ عَلَيْهِ فَلَمَّا رَأَى السَّيْفَ قَالَ لاَ إِلَهَ إِلاَّ اللَّهُ ‏.‏ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏"‏ أَقَتَلْتَهُ ‏"‏ ‏.‏ قَالَ نَعَمْ ‏.‏ قَالَ ‏"‏ فَكَيْفَ تَصْنَعُ بِلاَ إِلَهَ إِلاَّ اللَّهُ إِذَا جَاءَتْ يَوْمَ الْقِيَامَةِ ‏"‏ ‏.‏ قَالَ يَا رَسُولَ اللَّهِ اسْتَغْفِرْ لِي ‏.‏ قَالَ ‏"‏ وَكَيْفَ تَصْنَعُ بِلاَ إِلَهَ إِلاَّ اللَّهُ إِذَا جَاءَتْ يَوْمَ الْقِيَامَةِ ‏"‏ ‏.‏ قَالَ فَجَعَلَ لاَ يَزِيدُهُ عَلَى أَنْ يَقُولَ ‏"‏ كَيْفَ تَصْنَعُ بِلاَ إِلَهَ إِلاَّ اللَّهُ إِذَا جَاءَتْ يَوْمَ الْقِيَامَةِ ‏"‏ ‏.‏