Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) narrates: The Prophet (peace and blessings be upon him) sent Sayyiduna Abu Musa al-Ash'ari (may Allah be pleased with him) on a military expedition at sea. While they were at sea, on a dark night, when they had raised the sail, a caller called out from above them: "O people of the ship, stop! I will tell you of a decree that Allah Almighty has decreed upon Himself." Sayyiduna Abu Musa (may Allah be pleased with him) said: "Tell us, if you are going to tell." He said: "Indeed, Allah, the Blessed and Exalted, has decreed upon Himself that whoever keeps himself thirsty for the sake of Allah Almighty on a hot day (that is, fasts), Allah Almighty will quench his thirst on the Day of Thirst."
Al-Bazzar recorded it, and its narrators have been declared trustworthy.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصيام / 5095