كتاب الصلاة
2  
The Book of Prayer
Bulugh al-Maram 276
Abu Dawud reported a Hadith narrated by Abu Humaid (RA) to the effect that he [Allah's Messenger (ﷺ)] used to raise his hands and bring them parallel to his shoulders, and then utter the Takbir.
وَفِي حَدِيثِ أَبِي حُمَيْدٍ , عِنْدَ أَبِي دَاوُدَ : { يَرْفَعُ يَدَيْهِ حَتَّى يُحَاذِيَ بِهِمَا مَنْكِبَيْهِ, ثُمَّ يُكَبِّرَ } 1
Reference : Bulugh al-Maram 276
In-book reference : Book 2, Hadith 276
English translation : Book 2, Hadith 274
Hadith Text
Reference