Hisnul Muslim 183

To one offering a drink or to one who intended to do that

اللَّهُمَّ أَطْعِمْ مَنْ أَطْعَمَنِي، وَاسْقِ مَنْ سَقَانِي

Allaahumma 'at'im man 'at'amanee wasqi man saqaanee.

O Allah, feed the one who has fed me and drink to the one who has given me drink.