Book 3, Hadith 32

Yahya related to me from Malik from Sadaqa ibn Yasar that al- Mughira ibn Hakim saw Abdullah ibn Umar sit back from the two sajdas of the prayer onto the top of his feet. When he had finished, al- Mughira mentioned it to him, and Abdullah ibn Umar explained, "It is not a sunna of the prayer. I do it because I am ill