Mishkat al-Masabih 13 Marriage كتاب النكاح 166

وَعَن أنس قَالَ: آلى رَسُول الله مِنْ نِسَائِهِ شَهْرًا وَكَانَتِ انْفَكَّتْ رِجْلُهُ فَأَقَامَ فِي مَشْرُبَةٍ تِسْعًا وَعِشْرِينَ لَيْلَةً ثُمَّ نَزَلَ فَقَالُوا: يَا رَسُولَ اللَّهِ آلَيْتَ شَهْرًا فَقَالَ: «إِنَّ الشَّهْرَ يَكُونُ تِسْعًا وَعِشْرِينَ» . رَوَاهُ الْبُخَارِيُّ

Anas said that God’s Messenger swore he would stay away from his wives for a month. His foot being dislocated, he stayed in an upper room for twenty-nine nights and then came down; and when it was remarked to him that he has sworn to stay away for a month, he replied, “The month has twenty-nine days.”* *This is most probably with reference to the month in question, as it cannot be considered a general statement. Bukhari transmitted it.