بُلُوغُ الْمَرَامِ
Bulugh al-Maram 443
The Book of Prayer
وَعَنْ جَابِرٍ قَالَ: { عَادَ اَلنَّبِيُّ - صلى الله عليه وسلم -مَرِيضًا, فَرَآهُ يُصَلِّي عَلَى وِسَادَةٍ, فَرَمَى بِهَا, وَقَالَ: صَلِّ عَلَى اَلْأَرْضِ إِنْ اِسْتَطَعْتَ, وَإِلَّا فَأَوْمِ إِيمَاءً, وَاجْعَلْ سُجُودَكَ أَخْفَضَ مِنْ رُكُوعِكَ } رَوَاهُ اَلْبَيْهَقِيُّ. وَصَحَّحَ أَبُو حَاتِمٍ وَقْفَهُ.
Narrated Jabir (RA): The Prophet (ﷺ) visited a sick man and saw him praying on a cushion, he threw it away and said, "Pray on the ground, if you can, or else pray by gestures and make your prostration lower than your bowing." [al-Baihaqi reported it and Abu Hatim graded it Sahih (authentic) in Mawquf form (as a saying of a companion, i.e. Jabir)].
Sunnah.com reference: Book 2, Hadith 358