Sunan at-Tirmithiy كتاب الصوم باب ما جاء فى سرد الصوم

حَدَّثَنَا عَلِىُّ بْنُ حُجْرٍ حَدَّثَنَا إِسْمَاعِيلُ بْنُ جَعْفَرٍ عَنْ حُمَيْدٍ عَنْ أَنَسِ بْنِ مَالِكٍ أَنَّهُ سُئِلَ عَنْ صَوْمِ النَّبِىِّ صلى الله عليه وسلم قَالَ كَانَ يَصُومُ مِنَ الشَّهْرِ حَتَّى نَرَى أَنَّهُ لاَ يُرِيدُ أَنْ يُفْطِرَ مِنْهُ وَيُفْطِرُ حَتَّى نَرَى أَنَّهُ لاَ يُرِيدُ أَنْ يَصُومَ مِنْهُ شَيْئًا وَكُنْتَ لاَ تَشَاءُ أَنْ تَرَاهُ مِنَ اللَّيْلِ مُصَلِّيًا إِلاَّ رَأَيْتَهُ مُصَلِّيًا وَلاَ نَائِمًا إِلاَّ رَأَيْتَهُ نَائِمًا. قَالَ أَبُو عِيسَى هَذَا حَدِيثٌ حَسَنٌ صَحِيحٌ.
Anas Ibn-Mālik was asked about the Prophet's, peace and blessings of God be upon him, fasting. He replied, "He used to fast on so many days of the month that we thought he would not stop fasting until the end, and he used to leave fasting on so many days that we thought he would not fast any of the month. And if you wanted to see him praying at night you would be able to, and if you wanted to see him sleeping [at night] you would be able to (1)."
(1) This hadīth aims to show that the Prophet, peace and blessings of God be upon him, exercised moderation in voluntary fasting and night prayer, keeping to them at times and leaving them at others while avoiding any patterns when performing these acts of worship, lest people think they have to follow them.