Hadithcore
Riyad as-Salihin, 764

Abu Sa'id Al-Khudri (May Allah be pleased with him) reported:

The Messenger of Allah (ﷺ) 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 (ﷺ) replied, "Pour them out." Then the man said: "My thirst is not quenched with one draught." Messenger of Allah (ﷺ) said, "Then put away the cup from your mouth (in between three gulps), and take breath." <b>[At-Tirmidhi]</b>.

عن أبى سعيد الخدرى رضى الله عنه أن النبي صلى الله عليه وسلم نهى عن النفخ في الشراب، فقال رجل ‏:‏ القذاة أراها في الإناء‏؟‏ فقالب‏:‏ ‏"‏أهرقها‏"‏ قال‏:‏ إني لا أروى من نفس واحد‏؟‏ قال‏:‏ ‏"‏فأبن القدح إذاً عن فيك‏"‏.‏((رواه الترمذي))

References1 variant
In-Book Reference
Book 2, Hadith 38
Sharh · explanationclick to expand
<b>Guidance from the Hadiths:</b><br> 1) The Islamic Shariah is perfect in all aspects, even in the fine details concerning the etiquette of eating and drinking.<br> 2) The forbiddance to blow into the vessel, lest harmful things come out. So, this instruction is aimed at protecting health and warding off harms. Is there a legislation more sublime than Islam?!