Language:
كتاب الأذان
10  
Call to Prayers (Adhaan)
(84)
Chapter: To raise both hands while saying the Takbir [on opening As-Salat (the prayer)], and while bowing and on raising up the head (after bowing)
(84)
باب رَفْعِ الْيَدَيْنِ إِذَا كَبَّرَ وَإِذَا رَكَعَ وَإِذَا رَفَعَ
Sahih al-Bukhari 737

Narrated Abu Qilaba:

I saw Malik bin Huwairith saying Takbir and raising both his hands (on starting the prayers and raising his hands on bowing and also on raising his head after bowing. Malik bin Huwairith said, "Allah's Messenger (ﷺ) did the same."

حَدَّثَنَا إِسْحَاقُ الْوَاسِطِيُّ، قَالَ حَدَّثَنَا خَالِدُ بْنُ عَبْدِ اللَّهِ، عَنْ خَالِدٍ، عَنْ أَبِي قِلاَبَةَ، أَنَّهُ رَأَى مَالِكَ بْنَ الْحُوَيْرِثِ إِذَا صَلَّى كَبَّرَ وَرَفَعَ يَدَيْهِ، وَإِذَا أَرَادَ أَنْ يَرْكَعَ رَفَعَ يَدَيْهِ، وَإِذَا رَفَعَ رَأْسَهُ مِنَ الرُّكُوعِ رَفَعَ يَدَيْهِ، وَحَدَّثَ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم صَنَعَ هَكَذَا‏.‏
Reference : Sahih al-Bukhari 737
In-book reference : Book 10, Hadith 131
USC-MSA web (English) reference : Vol. 1, Book 12, Hadith 704
  (deprecated numbering scheme)