The Book of Prayers
حَدَّثَنَا يَحْيَى بْنُ يَحْيَى، قَالَ أَخْبَرَنَا عُبَيْدُ اللَّهِ بْنُ إِيَادٍ، عَنْ إِيَادٍ، عَنِ الْبَرَاءِ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " إِذَا سَجَدْتَ فَضَعْ كَفَّيْكَ وَارْفَعْ مِرْفَقَيْكَ " .Al-Bira' (b. 'Azib) reported:The Messenger of Allah (ﷺ) said. When you prostrate yourself, place the palms of your hands on the ground and raise your elbows
From Sahih Muslim, whose reports the scholars accept as authentic.