The Quran

إِنَّ الَّذينَ يُبايِعونَكَ إِنَّما يُبايِعونَ اللَّهَ يَدُ اللَّهِ فَوقَ أَيديهِم ۚ فَمَن نَكَثَ فَإِنَّما يَنكُثُ عَلىٰ نَفسِهِ ۖ وَمَن أَوفىٰ بِما عاهَدَ عَلَيهُ اللَّهَ فَسَيُؤتيهِ أَجرًا عَظيمًا

Ali Unal

Those who swear allegiance to you (O Messenger), swear allegiance to God only. God’s “Hand” is over their hands.¹ Whoever then breaks his oath, breaks his oath only to his own harm; and whoever fulfills what he has covenanted with God, He will grant him a tremendous reward.

This statement has two important meanings. As obedience to the Messenger, upon him be peace and blessings, means the same as obedience to God (4: 80), and his throwing at the enemy means the same as God’s throwing (8: 17), the Messenger’s hand being over the hand which he grasps in allegiance represents God’s Hand. (For God ‘hand’ or any other such term is metaphorical.) The other meaning is that God helps those who swear allegiance to the Messenger. So, here ‘hand’ signifies Power.