"We left our tribe Ghifar, who used to violate the sacred month. So I set out with my brother Unays and our mother." He then mentioned the story of his acceptance of Islam and his entry into Mecca. It includes the following.The Messenger of Allah ﷺ asked, "How long have you been here?"He said, "I replied, 'I have been here for thirty days and nights.'"The Prophet ﷺ asked, "Who has been feeding you?"He said, "I replied, 'I have had no food except the water of Zamzam, yet I have grown so stout that the folds of my belly have become creased, and I feel no pangs of hunger in my stomach.'"The Prophet ﷺ said, "It is indeed blessed. It is a nourishing food."The hadith continues at length.
خرجنا من قومنا غفار، وكانوا يحلون الشهر الحرام، فخرجت أنا وأخي أنيس وأننا- فذكر قصة إسلامه ودخوله مكة- وفيه: أن رسول الله ﷺ قال: متي كنت ههنا؟ قال: قلت: قد كنت ههنا منذ ثلاثين بين ليلة ويوم. قال: فمن كان يطعمك؟ قال: قلت: ما كان لي طعام إلا ماء زمزم، فسمنت حتى تكسرت عكن بطني، وما أجد على كبدي سخفة جوع، قال: إنها مباركة، إنها طعام طعم. الحديث بطوله.
Muslim narrated it in Fadail al-Sahabah (2473:132) from Haddab bin Khalid Azdi, who said, Sulayman bin Mughira narrated to us, Humayd bin Hilal informed us, from Abdullah bin Samit, who said, Abu Dharr said, "We set out from our tribe Ghifar," and he mentioned it. The hadith in full is mentioned in Fadail al-Sahabah, the chapter on the story of Abu Dharr's conversion to Islam.