It is narrated from Abd al-Rahman bin Zayd al-Ansari that Sayyiduna Anas bin Malik (may Allah be pleased with him) came from Iraq, and Sayyiduna Abu Talhah and Ubayy bin Ka'b (may Allah be pleased with them both) came to visit him. He served them food that had been cooked on fire. They ate from it; then Sayyiduna Anas (may Allah be pleased with him) stood up and performed ablution, whereupon Sayyiduna Abu Talhah and Sayyiduna Ubayy bin Ka'b (may Allah be pleased with them both) said: "O Anas! What is this, an Iraqi practice?" Sayyiduna Anas (may Allah be pleased with him) said: "I wish I had not done it." Sayyiduna Abu Talhah and Ubayy bin Ka'b (may Allah be pleased with them both) stood up and offered the prayer but did not perform ablution.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 734