صحيح ابن خزيمه
Sahih Ibn Khuzaymah
جماع أبواب صلاة التطوع قاعداChapters on Voluntary Prayers while Sitting
(560) بَابُ صِفَةِ صَلَاةِ الْمُضْطَجِعِThe chapter on the description of prayer while lying down
Hadith Q1250
خِلَافَ مَا يَتَوَهَّمُهُ الْعَامَّةُ إِذِ الْعَامَّةُ إِنَّمَا تَأْمُرُ الْمُصَلِّي مُضْطَجِعًا أَنْ يُصَلِّيَ مُسْتَلْقِيًا عَلَى قَفَاهُ، وَالنَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ أَمَرَ الْمُصَلِّي مُضْطَجِعًا أَنْ يُصَلِّيَ عَلَى جَنْبٍ
Contrary to the opinion of the public, because the public instructs the one who prays while lying down to pray while lying on his back, whereas the Noble Prophet (peace and blessings be upon him) instructed the one who prays while lying down to pray while lying on his side.
