It has been narrated on the authority of 'A'isha that Sa'd's wound became dry and was going to heal when he prayed:

O God, surely You knowest that nothing is dearer to me than that I should fight for Your cause against the people who disbeliever Your Messenger (ﷺ) and turned him out (from his native place). If anything yet remains to be decided from the war against the Quraish, spare my life so that I may fight against them in Your cause. O Lord, I think You have ended the war between us and them. If You have done so, open my wound (so that it may discharge) and cause my death thereby. So the wound begin to bleed from the front part of his neck. The people were not scared except when the blood flowed towards them, and in the mosque along with Sa'd's tent was the tent of Banu Ghifar. They said: O people of the tent, what is it that is coming to us from you? Lo! it was Sa'd's wound that was bleeding and he died thereof.

حَدَّثَنَا أَبُو كُرَيْبٍ، حَدَّثَنَا ابْنُ نُمَيْرٍ، عَنْ هِشَامٍ، أَخْبَرَنِي أَبِي، عَنْ عَائِشَةَ، أَنَّ سَعْدًا، قَالَ وَتَحَجَّرَ كَلْمُهُ لِلْبُرْءِ فَقَالَ اللَّهُمَّ إِنَّكَ تَعْلَمُ أَنْ لَيْسَ أَحَدٌ أَحَبَّ إِلَىَّ أَنْ أُجَاهِدَ فِيكَ مِنْ قَوْمٍ كَذَّبُوا رَسُولَكَ صلى الله عليه وسلم وَأَخْرَجُوهُ اللَّهُمَّ فَإِنْ كَانَ بَقِيَ مِنْ حَرْبِ قُرَيْشٍ شَىْءٌ فَأَبْقِنِي أُجَاهِدْهُمْ فِيكَ اللَّهُمَّ فَإِنِّي أَظُنُّ أَنَّكَ قَدْ وَضَعْتَ الْحَرْبَ بَيْنَنَا وَبَيْنَهُمْ فَإِنْ كُنْتَ وَضَعْتَ الْحَرْبَ بَيْنَنَا وَبَيْنَهُمْ فَافْجُرْهَا وَاجْعَلْ مَوْتِي فِيهَا ‏.‏ فَانْفَجَرَتْ مِنْ لَبَّتِهِ فَلَمْ يَرُعْهُمْ - وَفِي الْمَسْجِدِ مَعَهُ خَيْمَةٌ مِنْ بَنِي غِفَارٍ - إِلاَّ وَالدَّمُ يَسِيلُ إِلَيْهِمْ فَقَالُوا يَا أَهْلَ الْخَيْمَةِ مَا هَذَا الَّذِي يَأْتِينَا مِنْ قِبَلِكُمْ فَإِذَا سَعْدٌ جُرْحُهُ يَغِذُّ دَمًا فَمَاتَ مِنْهَا ‏.‏