Sunan an-Nasa'i, Hadith 1088 ⓘ
It was narrated that Ibn 'Umar said: "The Messenger of Allah used to raise his hands when he started to pray, and when he bowed, and when he stood up, but he did not do that when he prostrated."
أَخْبَرَنَا مُحَمَّدُ بْنُ عُبَيْدٍ الْكُوفِيُّ الْمُحَارِبِيُّ، قَالَ حَدَّثَنَا ابْنُ الْمُبَارَكِ، عَنْ مَعْمَرٍ، عَنِ الزُّهْرِيِّ، عَنْ سَالِمٍ، عَنِ ابْنِ عُمَرَ، قَالَ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يَرْفَعُ يَدَيْهِ إِذَا افْتَتَحَ الصَّلاَةَ وَإِذَا رَكَعَ وَإِذَا رَفَعَ وَكَانَ لاَ يَفْعَلُ ذَلِكَ فِي السُّجُودِ .
also referenced under: Book 12, Hadith 60 (In-Book) & Volume 2, Book 12, Hadith 1089 (DarusSalam)