Imam Malik : 186

و حَدَّثَنِي عَنْ مَالِك عَنْ صَدَقَةَ بْنِ يَسَارٍ عَنْ الْمُغِيرَةِ بْنِ حَكِيمٍ أَنَّهُ رَأَى عَبْدَ اللَّهِ بْنَ عُمَرَيَرْجِعُ فِي سَجْدَتَيْنِ فِي الصَّلَاةِ عَلَى صُدُورِ قَدَمَيْهِ فَلَمَّا انْصَرَفَ ذَكَرَ لَهُ ذَلِكَ فَقَالَ إِنَّهَا لَيْسَتْ سُنَّةَ الصَّلَاةِ وَإِنَّمَا أَفْعَلُ هَذَا مِنْ أَجْلِ أَنِّي أَشْتَكِي

It was narrated to me from Malik, from Sadaqah ibn Yasar, from Al-Mughirah ibn Hakim, that he saw Abdullah ibn Umar leaning on the tops of his feet each time he raised his head from prostration. When he finished, someone mentioned it to him, and he said, 'It is not the Sunnah of prayer. I do this because my legs are in pain.'