Abdullah bin Umar (RA) said that the Prophet (ﷺ) used to recite this dua at the beginning of his journey:

اَللَّهُ أَكْبَرُ، اَللَّهُ أَكْبَرُ، اَللَّهُ أَكْبَرُ، سُبْحَانَ الَّذِيْ سَخَّرَ لَنَا هَذَا وَمَا كُنَّا لَهُ مُقْرِنِيْنَ، وَإِنَّا إِلَى رَبِّنَا لَمُنْقَلِبُوْنَ اَللَّهُمَّ إِنَّا نَسْأَلُكَ فِي سَفَرِنَا هَذَا الْبِرَّ وَالتَّقْوَى وَمِنَ الْعَمَلِ مَا تَرْضَى، اَللَّهُمَّ هَوِّنْ عَلَيْنَا سَفَرَنَا هَذَا وَاطْوِ عَنَّا بُعْدَهُ، اَللَّهُمَّ أَنْتَ الصَّاحِبُ فِي السَّفَرِ وَالْخَلِيْفَةُ فِي الْأَهْلِ، اَللَّهُمَّ إِنِّيْ أَعُوْذُ بِكَ مِنْ وَعْثَاءِ السَّفَرِ، وَكَآبَةِ الْمَنْظَرِ، وَسُوْءِ الْمُنْقَلَبِ فِي الْمَالِ وَالْأَهْلِ

Allahu 'Akbar, Allahu 'Akbar, Allahu 'Akbar. Subhaanal-lathee sakhkhara lanaa haadhaa wa maa kunnaa lahu muqrineen. Wa 'innaa 'ilaa Rabbinaa lamunqaliboon. Allaahumma 'innaa nas'aluka fee safarinaa haadhal-birra wattaqwaa, waminal-'amali maa tardhaa, Allaahumma hawwin 'alaynaa safaranaa haadhaa watwi 'annaa bu'dahu, Allaahumma 'Antas-saahibu fis-safari, walkhaleefatu fil-'ahli, Allaahumma 'innee 'A'oodhu bika min wa'thaa'is-safari, wa ka-'aabatil-mandhari, wa soo'il-munqalabi fil-maali wal 'ahli

Allah is the Most Great (3 times). Glory is to Him Who has provided this for us though we could never have had it by our efforts. Surely, unto our Lord we are returning. O Allah, we ask You on this our journey for goodness and piety, and for works that are pleasing to You. O Allah, lighten this journey for us and make its distance easy for us. O Allah, You are our Companion on the road and the One in Whose care we leave our family. O Allah, I seek refuge in You from this journey's hardships, and from the wicked sights in store and from finding our family and property in misfortune upon returning. And when the Prophet (ﷺ) returned from his journey, he would recite it and add to it:

Reference: Muslim: 1342