Sufyan said, perhaps reporting from the Prophet ﷺ, "When a dog licks the vessel of one of you, let him wash it seven times."
حدثنا سفيان عن أبي الزناد عن الأعرج
سفيان: لعله عن النبي ﷺ إذا ولغ الكلب في إناء أحدكم فليغسله سبع غسلات
Its isnad is sahih, despite Sufyan's doubt about whether it is raised to the Prophet. But its being raised to the Prophet is established without doubt through the narration of others among the imams. Malik narrated it in Muwatta 34, from Abu Zinad, from Aaraj, from Abu Hurairah, that the Messenger of Allah ﷺ said, "If a dog drinks from the vessel of one of you, let him wash it seven times." Bukhari likewise narrated it, 1:239-240, and Muslim, 1:92, by way of Malik. Waligh means it drank with its tongue. Ibn Athir said, "Waligh most often occurs with predatory animals."7341m - Sufyan narrated to us, from Abu Zinad, from Aaraj, from Abu Hurairah, who said, "Perhaps it is from the Prophet ﷺ, 'If a dog laps from the vessel of one of you, let him wash it seven washings.'"Sahih (7341m). Its isnad is sahih, and it is a repetition of the hadith before it, in both isnad and wording. It is thus established twice over in all three original sources. What I think is that when Imam Ahmad read the first isnad, in which it says, "He said, perhaps it is from the Prophet," he saw that it was not clear who said this, so he did not know about the doubt regarding whether it was raised to the Prophet. So he repeated it again, this time stating it clearly and explaining it, saying in it, "Sufyan said."