Muwatta Imam Malik Book of Purity, Hadith 10b

Yahya related to me from Malik from Zayd ibn Aslam that the ayat "You who believe! When you rise for prayer wash your faces, and your arms to the elbows, and wipe over your heads and your feet up to the ankles," refers to rising from bed, meaning sleep.

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ زَيْدِ بْنِ أَسْلَمَ أَنَّ تَفْسِيرَ هَذِهِ الْآيَةِ {يَا أَيُّهَا الَّذِينَ آمَنُوا إِذَا قُمْتُمْ إِلَى الصَّلَاةِ فَاغْسِلُوا وُجُوهَكُمْ وَأَيْدِيَكُمْ إِلَى الْمَرَافِقِ وَامْسَحُوا بِرُءُوسِكُمْ وَأَرْجُلَكُمْ إِلَى الْكَعْبَيْنِ} أَنَّ ذَلِكَ «إِذَا قُمْتُمْ مِنَ الْمَضَاجِعِ - يَعْنِي النَّوْمَ -»