Riyad Us-Saliheen (Gardens of the Righteous)
Undesirability of blowing into the Vessel while Drinking
765. Abu Sa`id Al-Khudri (May Allah be pleased with him) reported: Messenger of Allah (PBUH) prohibited us blowing in the drinking water. A man said: "O Messenger of Allah! Sometimes I see some litter floating about on the surface. What should I do then?'' He (PBUH) replied, "Pour them out.'' Then the man said: "My thirst is not quenched with one draught.'' Messenger of Allah (PBUH) said, "Then put away the cup from your mouth (in between three gulps), and take breath.''
Commentary: If one sees straw or something like that in the water-vessel, he should not blow in the water. Messenger of Allah (PBUH) has forbidden it. Instead, some of the water or all the water should be poured out. Also, if his thirst is not quenched in a single breath, one should remove the vessel from his mouth. After taking breath, he should again drink water. To drink water in three breaths is preferable. However, in case of hot tea or milk, sipping is permissible, no matter if sips are in plenty.
766. Ibn `Abbas (May Allah be pleased with them) reported: The Prophet (PBUH) prohibited us from breathing into the drinking vessel or blowing onto.