Qur'an 48:10 · Al-Fath

إِنَّ ٱلَّذِينَ يُبَايِعُونَكَ إِنَّمَا يُبَايِعُونَ ٱللَّهَ يَدُ ٱللَّهِ فَوْقَ أَيْدِيهِمْ ۚ فَمَن نَّكَثَ فَإِنَّمَا يَنكُثُ عَلَىٰ نَفْسِهِۦ ۖ وَمَنْ أَوْفَىٰ بِمَا عَٰهَدَ عَلَيْهُ ٱللَّهَ فَسَيُؤْتِيهِ أَجْرًا عَظِيمًۭا

(10) Indeed, those who pledge allegiance to you, [O Muḥammad] - they are actually pledging allegiance to Allāh. The hand[1508] of Allāh is over their hands.[1509] So he who breaks his word only breaks it to the detriment of himself. And he who fulfills that which he has promised Allāh - He will give him a great reward.