Sunan an-Nasa'i 1032

أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا أَبُو عَوَانَةَ، عَنْ أَبِي يَعْفُورٍ، عَنْ مُصْعَبِ بْنِ سَعْدٍ، قَالَ صَلَّيْتُ إِلَى جَنْبِ أَبِي وَجَعَلْتُ يَدَىَّ بَيْنَ رُكْبَتَىَّ فَقَالَ لِي اضْرِبْ بِكَفَّيْكَ عَلَى رُكْبَتَيْكَ ‏.‏ قَالَ ثُمَّ فَعَلْتُ ذَلِكَ مَرَّةً أُخْرَى فَضَرَبَ يَدِي وَقَالَ إِنَّا قَدْ نُهِينَا عَنْ هَذَا وَأُمِرْنَا أَنْ نَضْرِبَ بِالأَكُفِّ عَلَى الرُّكَبِ ‏.‏

It was narrated that Mus'ab bin Sa'd said:"I prayed beside my father and I put my hands between my knees, and he told me: 'Put your hands on your knees.' Then I did that again and he struck my hands and said: 'We were forbidden to do that, and we were commanded to put our hands on our knees