Sunan Abi Dawud

Narrated Abdullah ibn Umar: When the Messenger of Allah (ﷺ) sat on his camel to go out on a journey, he said: ""Allah is Most Great"" three times. Then he said: ""Glory be to Him Who has made subservient to us, for we had not the strength for it, and to our Lord do we return. O Allah, we ask Thee in this journey of ours, uprightness, piety and such deeds as are pleasing to Thee. O Allah, make easy for us this journey of ours and make its length short for us. O Allah, Thou art the Companion in the journey, and the One Who looks after the family and property in our absence."" When he returned, he said these words adding: ""Returning, repentant, serving and praising our Lord."" The Prophet (ﷺ) and his armies said: ""Allah is Most Great"" when they went up to high ground; and when armies said: ""Allah is most Great"" when they went up to high ground; and when they descended, they said: ""Glory be to Allah."" So the prayer was patterned on that