The Prophet (peace and blessings be upon him) said:
"Indeed, it (Zamzam water) is greatly blessed; it is excellent nourishment for the one who eats it."
Hadith Referenceصحیح الجامع الصغیر / حرف الألف / 2438
Hadith Gradingالألبانی:صحيح
Hadith Takhrij[حم م] عن أبي ذر. مختصر مسلم ١٧٠٤: طب.