Sunan of Abu Dawood Book 15, Hadith 2643

حَدَّثَنَا الْحَسَنُ بْنُ عَلِيٍّ، وَعُثْمَانُ بْنُ أَبِي شَيْبَةَ الْمَعْنَى، قَالاَ حَدَّثَنَا يَعْلَى بْنُ عُبَيْدٍ، عَنِ الأَعْمَشِ، عَنْ أَبِي ظَبْيَانَ، حَدَّثَنَا أُسَامَةُ بْنُ زَيْدٍ، قَالَ بَعَثَنَا رَسُولُ اللَّهِ صلى الله عليه وسلم سَرِيَّةً إِلَى الْحُرَقَاتِ فَنَذِرُوا بِنَا فَهَرَبُوا فَأَدْرَكْنَا رَجُلاً فَلَمَّا غَشَيْنَاهُ قَالَ لاَ إِلَهَ إِلاَّ اللَّهُ فَضَرَبْنَاهُ حَتَّى قَتَلْنَاهُ فَذَكَرْتُهُ لِلنَّبِيِّ صلى الله عليه وسلم فَقَالَ ‏"‏ مَنْ لَكَ بِلاَ إِلَهَ إِلاَّ اللَّهُ يَوْمَ الْقِيَامَةِ ‏"‏ ‏.‏ فَقُلْتُ يَا رَسُولَ اللَّهِ إِنَّمَا قَالَهَا مَخَافَةَ السِّلاَحِ ‏.‏ قَالَ ‏"‏ أَفَلاَ شَقَقْتَ عَنْ قَلْبِهِ حَتَّى تَعْلَمَ مِنْ أَجْلِ ذَلِكَ قَالَهَا أَمْ لاَ مَنْ لَكَ بِلاَ إِلَهَ إِلاَّ اللَّهُ يَوْمَ الْقِيَامَةِ ‏"‏ ‏.‏ فَمَا زَالَ يَقُولُهَا حَتَّى وَدِدْتُ أَنِّي لَمْ أُسْلِمْ إِلاَّ يَوْمَئِذٍ ‏.‏

Usamah bin Zaid said "The Messenger of Allah (ﷺ) sent us with a detachment to Al Huruqat. They learnt about us and fled away. But we found a man, when we attacked him he uttered "There is no god but Allaah, still we struck him till we killed him." When I mentioned it to the Prophet (ﷺ) he said "Who will save you from "There is no god but Allaah" on the Day of Judgment? I said "Messenger of Allah (ﷺ), he uttered it for the fear of the weapon." He said "Did you tear his heart so that you learnt whether he actually uttered it for this or not. Who will support you against "There is no god but Allaah"? He kept on repeating this till I wished I would have embraced Islam on that day