Question
What is the ruling for someone who began praying with tayammum due to the lack of water, and then was informed that water was being brought while he was in prayer?
Answer
I say, and with God's success: His tayammum is invalid, and he must perform ablution and repeat the prayer; because the ability to access water nullifies tayammum even if he is in prayer. See: Al-Bahr Al-Ra'iq 1: 160, and Rad Al-Muhtar 1: 170, and God knows best.