Mishkat al-Masabih 7 Fasting كتاب الصوم 147

عَنِ ابْنِ عُمَرَ عَنِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ أَنَّهُ كَانَ إِذَا اعْتَكَفَ طُرِحَ لَهُ فِرَاشُهُ أَوْ يُوضَعُ لَهُ سَرِيرُهُ وَرَاءَ أسطوانه التَّوْبَة. رَوَاهُ ابْن مَاجَه

Ibn ‘Umar said that when the Prophet observed a period of private devotion in the mosque his bedding was placed for him, or a couch was put down for him, behind the column of repentance.* *A column in the Prophet’s mosque in Medina, said to have got this name because the repentance of Abu Lubaba was accepted beside it. Ibn Majah transmitted it.