Musannaf Ibn Abi Shayba 36:281

Abu Khalid al-Ahmar narrated to us, from Yahya ibn Sa'id, from Sa'id ibn al-Musayyib, from Umar ibn al-Khattab, that the Messenger of Allah (may Allah bless him and grant him peace) did not pray the Dhuhr and Asr prayers on the day of the Trench until the sun had set.