The presence of the Prophet is a guarantee of peace for his people

وَمَا كَانَ ٱللَّهُ لِيُعَذِّبَهُمْ وَأَنتَ فِيهِمْ ۚ وَمَا كَانَ ٱللَّهُ مُعَذِّبَهُمْ وَهُمْ يَسْتَغْفِرُونَ

But Allah was not going to send them a penalty whilst thou wast amongst them; nor was He going to send it whilst they could ask for pardon.

قُلْ أَرَءَيْتُمْ إِنْ أَهْلَكَنِىَ ٱللَّهُ وَمَن مَّعِىَ أَوْ رَحِمَنَا فَمَن يُجِيرُ ٱلْكَٰفِرِينَ مِنْ عَذَابٍ أَلِيمٍۢ

Say: "See ye?- If Allah were to destroy me, and those with me, or if He bestows His Mercy on us,- yet who can deliver the Unbelievers from a grievous Penalty?"