It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) appointed Sayyiduna Abu Musa (may Allah be pleased with him) as commander of a naval expedition. While they were travelling by night, suddenly a caller called out to them from above: "Shall I not inform you of a decree which Allah has made binding upon Himself? Whoever remains thirsty for the sake of Allah on a scorching hot day, it is a right upon Allah that He will quench his thirst on the Day of Thirst (the Day of Resurrection)." This hadith has an authentic (sahih) chain of narration, but the two Shaykhs (Bukhari and Muslim) did not record it.