رِيَاضُ الصَّالِحِينَ
Riyad as-Salihin 765
The Book About the Etiquette of Eating
Undesirability of Blowing into the Vessel while Drinking
وَعَنِ ابْنِ عَبَّاسٍ رضى اللَّهُ عَنْهُمَا أَنَّ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ نَهَى أَنْ يُتَنَفَّسَ فِي الإِنَاءِ، أَوْ يُنْفَخَ فِيهِ.((رَوَاهُ التِّرْمِذِيّ))
Ibn 'Abbas (May Allah be pleased with them) reported: The Prophet (ﷺ) prohibited us from breathing into the drinking vessel or blowing in it. [At-Tirmidhi].
Riyad as-Salihin, 765