مُسْنَدُ أَحْمَدَ
Musnad Ahmad 1873
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated that Ibn ‘Abbas said: The Messenger of Allah (ﷺ) used to put two prayers together when travelling: Maghrib and "Isha", and Zuhr and "Asr.
Musnad Ahmad 1874Sahih hadeeth]