اللّهُـمَّ أَطْعِمْ مَن أَطْعَمَني، وَاسْقِ مَن سقاني.
Allahumma atAAim man atAAamanee wasqi man saqanee.
Translation
O Allah, feed him who fed me, and provide with drink him who provided me with drink.
When to recite
Said for someone who gives you a drink.