Reference: Sharh ‘Umdatil-Fiqh – Tape 1, Question No.30
Question: If the time for prayer has arrived, and there is no pure water – just impure water, would it be permissible to purify myself with this impure water, or should I [suffice with] do[ing] tayammum?
Response: No, don’t purify yourself with impure water. [The ruling regarding] impure water [is that it] is to be treated as if there is no water. [That being the case], do tayammum, then pray.