مُوَطَّأُ مَالِكٍ
Muwatta Malik 394
Shortening the Prayer
وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ نَافِعٍ، أَنَّ عَبْدَ اللَّهِ بْنَ عُمَرَ، كَانَ يَقُولُ مَنْ وَضَعَ جَبْهَتَهُ بِالأَرْضِ فَلْيَضَعْ كَفَّيْهِ عَلَى الَّذِي يَضَعُ عَلَيْهِ جَبْهَتَهُ ثُمَّ إِذَا رَفَعَ فَلْيَرْفَعْهُمَا فَإِنَّ الْيَدَيْنِ تَسْجُدَانِ كَمَا يَسْجُدُ الْوَجْهُ .
Yahya related to me from Malik from Nafi that Abdullah ibn Umar used to say, "When one of you puts his forehead on the ground he should put his palms on the place where he puts his forehead. Then, when he rises, he should raise them, for the hands prostrate just as the face prostrates."
Arabic/English book reference: Book 9, Hadith 63