"The Prophet swore an oath of abstention from his wives for a month and stayed in his room for twenty-nine days. It was said: 'O Messenger of Allah, did you not swear an oath of abstention for a month?' He said: 'This month is twenty-nine days.'" (Using translation from Nasāʾī 3456)
آلَى النَّبِيُّ ﷺ مِنْ نِسَائِهِ شَهْرًا فَقَعَدَ فِي مَشْرُبَةٍ لَهُ فَمَكَثَ تِسْعًا وَعِشْرِينَ لَيْلَةً ثُمَّ نَزَلَ فَقِيلَ يَا رَسُولَ اللهِ أَلَسْتَ آلَيْتَ عَلَى شَهْرٍ؟ قَالَ «الشَّهْرُ تِسْعٌ وَعِشْرُونَ»