Al-Fath 48:10

Those who pledge allegiance to you [O Prophet] are indeed pledging allegiance to Allah; Allah’s Hand is over their hands[4]. Whoever breaks his pledge, he only breaks it to his own detriment, but whoever fulfills his covenant with Allah, He will give him a great reward.

[4] i.e., Allah Almighty approved their pledge.

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.

[1508] See footnote to 2:19.
[1509] Meaning that He (subḥānahu wa taʿālā) accepted their pledge.

10. Verily, those who give Bai‘ah (pledge) to you (O Muhammad صلى الله عليه وسلم) they are giving Bai‘ah (pledge) to Allâh. The Hand of Allâh is over their hands. Then whosoever breaks his pledge, breaks it only to his own harm; and whosoever fulfils what he has covenanted with Allâh, He will bestow on him a great reward.

Lo! those who swear allegiance unto thee (Muhammad), swear allegiance only unto Allah. The Hand of Allah is above their hands. So whosoever breaketh his oath, breaketh it only to his soul's hurt; while whosoever keepeth his covenant with Allah, on him will He bestow immense reward.