Humaid ibn Anas ibn Malik reported that he was asked about the fasting of the Prophet (ﷺ), so he said:

"He used to fast during the month until we would assume that he did not intend to break fast during it, and he used to break fast until we would assume that he did not intend to fast during any of it. You would not wish to assume that he was performing the ritual prayer during the night, unless you saw him performing the ritual prayer, nor that he was sleeping, unless you saw him sleeping.”

حَدَّثَنَا عَلِيُّ بْنُ حُجْرٍ، قَالَ‏:‏ حَدَّثَنَا إِسْمَاعِيلُ بْنُ جَعْفَرٍ، عَنْ حُمَيْدٍ، عَنْ أَنَسِ بْنِ مَالِكٍ، أَنَّهُ سُئِلَ عَنْ صَوْمِ النَّبِيِّ صلى الله عليه وسلم، فَقَالَ‏:‏ كَانَ يَصُومُ مِنَ الشَّهْرِ حَتَّى نَرَى أَنْ لا يُرِيدَ أَنْ يُفْطِرَ مِنْهُ، وَيُفْطِرُ مِنْهُ حَتَّى نَرَى أَنْ لا يُرِيدَ أَنْ يَصُومَ مِنْهُ شَيْئًا وَكُنْتَ لا تَشَاءُ أَنْ تَرَاهُ مِنَ اللَّيْلِ مُصَلِّيًا إِلا رَأَيْتَهُ مُصَلِّيًا، وَلا نَائِمًا إِلا رَأَيْتَهُ نَائِمًا‏.‏