Surah Al-Fath, ayah 10

إِنَّ ٱلَّذِينَ يُبَايِعُونَكَ إِنَّمَا يُبَايِعُونَ ٱللَّهَ يَدُ ٱللَّهِ فَوۡقَ أَيۡدِيهِمۡۚ فَمَن نَّكَثَ فَإِنَّمَا يَنكُثُ عَلَىٰ نَفۡسِهِۦۖ وَمَنۡ أَوۡفَىٰ بِمَا عَٰهَدَ عَلَيۡهُ ٱللَّهَ فَسَيُؤۡتِيهِ أَجۡرًا عَظِيمٗا ١٠

Innal-ladhīna yubāyi'ūnaka innamā yubāyi'ūnallāha yadullāhi fawqa aydīhim faman nakatha fa innamā yankuthu 'alā nafsihī waman awfā bimā 'āhada 'alayhullāha fasayu'tīhi ajran 'azīmā

Indeed, those who pledge allegiance to you, [O Muḥammad] - they are actually pledging allegiance to Allāh. The hand¹⁵⁰⁸ 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.