The Shaykh (Al-Mufid), may Allah سبحانه وتعالى support him, narrated to me from Abu Ja'far Muhammad ibn Ali, from Muhammad ibn Al-Hasan, from Muhammad ibn Yahya, from Muhammad ibn Ahmad ibn Yahya, from Ahmad ibn Al-Hasan ibn Ali ibn Faddal, from Amr ibn Sa'id, from Musaddiq ibn Sadaqah, from Ammar Al-Sabati, from Abu Abdullah عليه السلام in a lengthy narration. He said: Imam عليه السلام was asked about a man who has two containers of water, and impurity falls into one of them, but he does not know which one it is, and he has no other water available. Imam عليه السلام said: "He must pour out both of them and perform Tayammum."