Language:
كتاب الأذان
10  
Call to Prayers (Adhaan)
(83)
Chapter: To raise both hands on saying the first Takbir simultaneously with opening the Salat (prayer)
(83)
باب رَفْعِ الْيَدَيْنِ فِي التَّكْبِيرَةِ الأُولَى مَعَ الاِفْتِتَاحِ سَوَاءً
Sahih al-Bukhari 735

Narrated Salim bin `Abdullah:

My father said, "Allah's Messenger (ﷺ) used to raise both his hands up to the level of his shoulders when opening the prayer; and on saying the Takbir for bowing. And on raising his head from bowing he used to do the same and then say "Sami`a l-lahu liman hamidah, Rabbana wa laka l-hamd." And he did not do that (i.e. raising his hands) in prostrations.

حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مَسْلَمَةَ، عَنْ مَالِكٍ، عَنِ ابْنِ شِهَابٍ، عَنْ سَالِمِ بْنِ عَبْدِ اللَّهِ، عَنْ أَبِيهِ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ يَرْفَعُ يَدَيْهِ حَذْوَ مَنْكِبَيْهِ إِذَا افْتَتَحَ الصَّلاَةَ، وَإِذَا كَبَّرَ لِلرُّكُوعِ، وَإِذَا رَفَعَ رَأْسَهُ مِنَ الرُّكُوعِ رَفَعَهُمَا كَذَلِكَ أَيْضًا وَقَالَ ‏ "‏ سَمِعَ اللَّهُ لِمَنْ حَمِدَهُ، رَبَّنَا وَلَكَ الْحَمْدُ ‏"‏‏.‏ وَكَانَ لاَ يَفْعَلُ ذَلِكَ فِي السُّجُودِ‏.‏
Reference : Sahih al-Bukhari 735
In-book reference : Book 10, Hadith 129
USC-MSA web (English) reference : Vol. 1, Book 12, Hadith 702
  (deprecated numbering scheme)