After returning the salutation, Rasulullah (ﷺ) would say once:
اَللَّهُ اَكْبَرُ
Pronunciation
Allahu 'Akbar
Meaning
Allah is the greatest.
Source: Bukhari: 842
Read the hadith
حَدَّثَنَا عَلِيُّ بْنُ عَبْدِ اللَّهِ، قَالَ حَدَّثَنَا سُفْيَانُ، {عَنْ عَمْرٍو،} قَالَ أَخْبَرَنِي أَبُو مَعْبَدٍ، عَنِ ابْنِ عَبَّاسٍ ـ رضى الله عنهما ـ قَالَ كُنْتُ أَعْرِفُ انْقِضَاءَ صَلاَةِ النَّبِيِّ صلى الله عليه وسلم بِالتَّكْبِيرِ.
Narrated Ibn `Abbas: I used to recognize the completion of the prayer of the Prophet (ﷺ) by hearing Takbir. [Bukhari: 842]
Duas from IslamicAPI's Masnun Dua dataset (based on the Quran, hadith, Hisnul Muslim and Rahe Belayat). See the dataset