Sahih Bukhari Volume 5, Book 64, Hadith 4118

حَدَّثَنَا مُحَمَّدُ بْنُ مُقَاتِلٍ، أَخْبَرَنَا عَبْدُ اللَّهِ، أَخْبَرَنَا مُوسَى بْنُ عُقْبَةَ، عَنْ سَالِمٍ، وَنَافِعٍ، عَنْ عَبْدِ اللَّهِ ـ رضى الله عنه ـ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ إِذَا قَفَلَ مِنَ الْغَزْوِ، أَوِ الْحَجِّ، أَوِ الْعُمْرَةِ، يَبْدَأُ فَيُكَبِّرُ ثَلاَثَ مِرَارٍ ثُمَّ يَقُولُ ‏"‏ لاَ إِلَهَ إِلاَّ اللَّهُ وَحْدَهُ لاَ شَرِيكَ لَهُ، لَهُ الْمُلْكُ وَلَهُ الْحَمْدُ، وَهْوَ عَلَى كُلِّ شَىْءٍ قَدِيرٌ، آيِبُونَ تَائِبُونَ عَابِدُونُ سَاجِدُونَ، لِرَبِّنَا حَامِدُونَ، صَدَقَ اللَّهُ وَعْدَهُ، وَنَصَرَ عَبْدَهُ، وَهَزَمَ الأَحْزَابَ وَحْدَهُ ‏"‏‏

Narrated By 'Abdullah : Whenever Allah's Apostle returned from a Ghazwa, Hajj or 'Umra, he used to start (saying), "Allahu-Akbar," thrice and then he would say, "None has the right to be worshipped except Allah alone Who has no partners. To Him belongs the Kingdom, all praises are for Him, and He is able to do all things (i.e. Omnipotent). We are returning with repentance (to Allah) worshipping, prostrating, and praising our Lord. Allah has fulfilled His Promise, made His Slave victorious, and He (Alone) defeated the clans (of infidels)."