كتاب الطهارة
Read the English translation first, with the original Arabic directly underneath.
It was narrated from Abu Qatadah that the Messenger of Allah (ﷺ) said:
"When any one of you drinks, let him not breathe into the vessel, and when he goes to the toilet let him not touch his penis with his right hand, nor wipe himself with this right hand."
إِذَا شَرِبَ أَحَدُكُمْ فَلاَ يَتَنَفَّسْ فِي إِنَائِهِ وَإِذَا أَتَى الْخَلاَءَ فَلاَ يَمَسَّ ذَكَرَهُ بِيَمِينِهِ وَلاَ يَتَمَسَّحْ بِيَمِينِهِ