On a high place, Allah's Messenger ﷺ would say Allahu Akbar three times, then say this supplication:

لَآ اِلٰهَ اِلَّا اللّٰهُ وَحْدَهٗ لَا شَرِيْكَ لَهٗ ، لَهُ الْمُلْكُ وَلَهُ الْحَمْدُ وَهُوَ عَلٰى كُلِّ شَيْءٍ قَدِيْرٌ آيِبُوْنَ تَائِبُوْنَ عَابِدُوْنَ لِرَبِّنَا حَامِدُوْنَ صَدَقَ اللّٰهُ وَعْدَهٗ وَنَصَرَ عَبْدَهٗ وَهَزَمَ الْاَحْزَابَ وَحْدَهٗ

There is no deity except Allah; He is alone and has no partner. His is the dominion and His is all praise, and He has full power over all things. We are returning, repenting, worshipping (and) praising our Lord. Allah has fulfilled His promise, helped His servant, and alone defeated all the (opposing) groups.

Sahih al-Bukhari, no. (6385), the wording is his, Sahih Muslim, no. (1344), Sunan Abi Dawud, no. (2770), Sunan at-Tirmidhi, no. (950).