Surah Al-Fath, Verse 10
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
Translation — Sahih International
Indeed, those who pledge allegiance to you, [O Muhammad] - they are actually pledging allegiance to Allah. The hand of Allah is over their hands. So he who breaks his word only breaks it to the detriment of himself. And he who fulfills that which he has promised Allah - He will give him a great reward.
Source
Kur'an-ı Kerim, Fetih Suresi 48:10
https://kuran.diyanet.gov.tr/mushaf/kuran-meal-2/48-suresi-10-ayet