Language:
كتاب الأذان
10  
Call to Prayers (Adhaan)
(115)
Chapter: Itmam At-Takbir (i.e., to end the number of Takbir or to say the Takbir perfectly) on bowing. [See Fath Al-Bari]
(115)
باب إِتْمَامِ التَّكْبِيرِ فِي الرُّكُوعِ
Sahih al-Bukhari 785

Narrated Abu Salama:

When Abu Huraira led us in prayer he used to say Takbir on each bowing and rising. On the completion of the prayer he used to say, "My prayer is more similar to the prayer of Allah's Messenger (ﷺ) than that of anyone of you."

حَدَّثَنَا عَبْدُ اللَّهِ بْنُ يُوسُفَ، قَالَ أَخْبَرَنَا مَالِكٌ، عَنِ ابْنِ شِهَابٍ، عَنْ أَبِي سَلَمَةَ، عَنْ أَبِي هُرَيْرَةَ، أَنَّهُ كَانَ يُصَلِّي بِهِمْ، فَيُكَبِّرُ كُلَّمَا خَفَضَ وَرَفَعَ، فَإِذَا انْصَرَفَ قَالَ إِنِّي لأَشْبَهُكُمْ صَلاَةً بِرَسُولِ اللَّهِ صلى الله عليه وسلم‏.‏
Reference : Sahih al-Bukhari 785
In-book reference : Book 10, Hadith 180
USC-MSA web (English) reference : Vol. 1, Book 12, Hadith 752
  (deprecated numbering scheme)