إِذَا شَرِبَ الْكَلْبُ فِي إِنَاءِ أَحَدِكُمْ فَلْيَغْسِلْهُ سَبْعَ مَرَّاتٍ (Mishkat al-Masabih, 490)
Meaning: When a dog drinks from a vessel belonging to any of you, he should wash it seven times.
This wording gives the instruction to wash the vessel seven times.