كتاب الصلاة
2  
The Book of Prayer
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


‏1 ‏- صحيح .‏ رواه أبو داود (730)‏ .‏

Sunnah.com reference : Book 2, Hadith 156
English translation : Book 2, Hadith 274
Arabic reference : Book 2, Hadith 276