Qutaybah bin Sa'id (may Allah have mercy on him) says that I asked the caretaker of the well of Buda'ah about its depth, and he said: At most the water in it reaches the pubic region. I said: And when it decreases? He said: Below the private parts. Imam Abu Dawud (may Allah have mercy on him) says: I estimated the well of Buda'ah with my cloak; I spread it over it and then measured it, and its width was six cubits. I asked the man who had opened the gate of the garden for me and let me in: Has its structure been changed from what it was before? He said: No. I saw water in it whose colour had changed.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 1261