The narration reported by Ahmad ibn Muhammad ibn Abi Nasr al-Bazanti, who said Muhammad ibn Sama‘ah narrated to me, from Muhammad ibn Humran, from Abu Abdullah عليه السلام: I asked Imam عليه السلام about a man who performed tayammum and then entered the prayer after having searched for water but could not find it. Then, while he is in the prayer, water is brought to him. Imam عليه السلام said: 'He should continue in the prayer. And know that no one should perform tayammum except at the end of the prayer time.'"