Musnad Ahmad 27:1184

Yahya ibn Adam narrated to us, Hasan—meaning Ibn Salih—narrated to us, from Firas, from Atiyyah al-Awfi, from Ibn Umar, who said: I prayed with the Messenger of Allah, may Allah bless him and grant him peace, while at home and while traveling. He prayed Dhuhr at home as four rak'ahs, and after it two rak'ahs. He prayed Asr as four rak'ahs, and there is nothing after it. He prayed Maghrib as three rak'ahs, and after it two rak'ahs. He prayed Isha as four rak'ahs. He prayed Dhuhr while traveling as two rak'ahs, and after it two rak'ahs. He prayed Asr as two rak'ahs, and there is nothing after it. He prayed Maghrib as three rak'ahs, and after it two rak'ahs. He prayed Isha as two rak'ahs, and after it two rak'ahs.