Musnad Ahmad 25:1621

'Abd al-Razzaq narrated to us, he said: Ibn Jurayj informed us, he said: Husayn ibn 'Abd Allah ibn 'Ubayd Allah ibn 'Abbas informed me, from 'Ikrimah and from Kurayb, that Ibn 'Abbas said: "Shall I not tell you about the prayer of the Messenger of Allah, peace and blessings of Allah be upon him, while traveling?" We said: "Yes." He said: "When the sun declined while he was at his stopping place, he would combine the Dhuhr and the 'Asr before he mounted. And if it did not decline while he was at his stopping place, he would travel until, when the time for 'Asr arrived, he would descend and combine the Dhuhr and the 'Asr. And when the Maghrib time arrived while he was at his stopping place, he would combine it with the 'Isha. And if it did not arrive while he was at his stopping place, he would mount until, when the time for 'Isha arrived, he would descend and combine them."