Hisn al-Muslim · Book 1 · Hadith 183
اللّهُـمَّ أَطْعِمْ مَن أَطْعَمَني، وَاسْقِ مَن سقاني
Allāhumma aṭ`im man aṭ`amanī wasqi man saqānī. O Allah, feed the one who has fed me, and give drink to the one who has given me drink. Reference: Muslim 3/126.