عن عبد الله بن عمر رضي الله عنهما أن النبي صلى الله عليه وسلم كان يرفع يديه حَذْوَ مَنْكِبَيْهِ إذا افْتَتَحَ الصلاة، وإذا كبّر للرُّكُوعِ ، وإذا رفع رأسه من الركوع رَفَعَهُمَا كذلك، وقال: سَمِعَ الله لمن حَمِدَهُ رَبَّنَا ولك الحمد، وكان لا يفعل ذلك في السُّجُودِ.
[صحيح] - [متفق عليه]
‘Abdullāh ibn ‘Umar (may Allah be pleased with him) reported: The Prophet (may Allah's peace and blessings be upon him) used to raise his hands to the level of his shoulders when he commenced the prayer, when he said Takbīr before bowing, and when he raised his head after bowing, he would raise them to that level as well, and say: "Allah hears him who praises Him. Our Lord, for You is all praise" and he did not use to do that in prostration.
Sahih/Authentic. - [Al-Bukhari and Muslim]
Prayer is a great act of worship, in which each organ of the body is involved. The hands, for instance, have a role in the prayer like raising them while reciting Takbīr al-Ihrām, or the commencement Takbīr, which is an adornment for the prayer and a glorification of Allah, the Almighty. The hands are raised up to the shoulders. They are also raised before bowing and when raising the head from bowing in each Rak‘ah of the prayer. In this Hadīth, the narrator explicitly states that the Prophet (may Allah's peace and blessings be upon him) did not do that in prostration since it is an act of going down and descending.