Muwatta Malik Book 9, Hadith 7
Yahya related to me from Malik from Ibn Shihab that he had asked
Salim ibn Abdullah, "Can you join dhuhr and asr when travelling?" He
said, "Yes, there is no harm in that. Haven't you seen the people pray
on Arafa?"
Yahya related to me from Malik from Nafi that Abdullah ibn Umar used to join the prayer along with the amirs if they joined maghrib and isha in the rain.
Yahya related to me from Malik that he had heard that AIi ibn Husain used to say, "The Messenger of Allah, may Allah bless him and grant him peace, would join dhuhr and asr if he wished to travel the same day, and he would join maghrib and isha if he wished to travel the same night."