كتاب الصيام
Read the English translation first, with the original Arabic directly underneath.
Umm Salama (Allah be pleased with him) reported that the Messenger of Allah (ﷺ) took an oath that he would not go to some of his wives for the whole of the month. When twenty-nine days bad passed he (the Prophet) went to them in the morning or in the evening. Upon this it was said to him:
Messenger of Allah, you took an oath that you would not come to us for a month, whereupon he said: The month may also consist of twenty-nine days.
إِنَّ الشَّهْرَ يَكُونُ تِسْعَةً وَعِشْرِينَ يَوْمًا