It is narrated from Abu Sa'id Khudri (may Allah be pleased with him) that the Prophet Muhammad (peace and blessings be upon him) forbade blowing into a drinking vessel. A man asked: "If I see something undesirable in the vessel, what should I do?" He replied: "Pour it out." The man said: "I cannot quench my thirst in one breath." He said: "Then remove the cup from your mouth when you breathe." Imam Tirmidhi says: This hadith is Hasan Sahih.