Musnad Ahmad 32:551

Hujayn narrated to us, Abd al-Aziz narrated to us, from Muhammad ibn Abi Bakr al-Thaqafi, from Anas ibn Malik, who said: "We were with the Messenger of Allah, may Allah bless him and grant him peace, on the morning of Arafah. Among us were those who were saying the takbir (Allahu Akbar), and among us were those who were saying the tahlil (La ilaha illa Allah). The one saying the takbir was not criticized for his takbir, nor was the one saying the tahlil criticized for his tahlil."