Sunan an-Nasa'i, Hadith 1033 ⓘ
It was narrated that Mus'ab bin Sa'd said: "I bowed and put my hands together, and my father said: 'This is something that we used to do, then we brought them up to our knees.'"
أَخْبَرَنَا عَمْرُو بْنُ عَلِيٍّ، قَالَ حَدَّثَنَا يَحْيَى بْنُ سَعِيدٍ، عَنْ إِسْمَاعِيلَ بْنِ أَبِي خَالِدٍ، عَنِ الزُّبَيْرِ بْنِ عَدِيٍّ، عَنْ مُصْعَبِ بْنِ سَعْدٍ، قَالَ رَكَعْتُ فَطَبَّقْتُ فَقَالَ أَبِي إِنَّ هَذَا شَىْءٌ كُنَّا نَفْعَلُهُ ثُمَّ ارْتَفَعْنَا إِلَى الرُّكَبِ .
also referenced under: Book 12, Hadith 5 (In-Book) & Volume 2, Book 12, Hadith 1034 (DarusSalam)