The Messenger of Allah ﷺ used to prostrate and sleep (in prostration) and produce puffing sounds (during sleep). Then he would stand and pray and would not perform ablution. I said to him: you prayed but did not perform ablution though you slept (in prostration). He replied: Ablution is necessary for one who sleeps while he is lying down. Uthman and Hannad added: For when he lies down, his joints are relaxed. Abu Dawud said: The statement "ablution is necessary for one who sleeps while one is lying down" is a munkar (rejected) tradition. It has been narrated only by Yazid Abu Khalid al-Dalani, on the authority of Qatadah. And its earlier part has been narrated by a group (of narrators) from Ibn 'Abbas; they did not mention anything about it. He (Ibn 'Abbas) said: The Prophet ﷺ was protected (during his sleep). 'Aishah reported: The Prophet ﷺ said: My eyes sleep, but my heart does not sleep. Shu'bah said: Qatadah heard from Abu'l-'Aliyah only four traditions: the tradition about Jonah son of Matthew, the tradition reported by Ibn 'Umar about prayer, the tradition stating that the judges are three, and the tradition narrated by Ibn 'Abbas saying: (This tradition) has been narrated to me by reliable persons ; 'Umar is one of them, and the most reliable of them in my opinion is 'Umar. Abu Dawud said: I asked Ahmad b. Hanbal about the tradition narrated by Yazid al-Dalani. He rebuked me out of respect for him. Then he said: Yazid al-Dalani does not add anything to what has been narrated by the teachers of Qatadah. He did not care of this tradition (due to its weakness).  

أَنَّ رَسُولَ اللَّهِ ﷺ كَانَ يَسْجُدُ وَيَنَامُ وَيَنْفُخُ ثُمَّ يَقُومُ فَيُصَلِّي وَلاَ يَتَوَضَّأُ قَالَ فَقُلْتُ لَهُ صَلَّيْتَ وَلَمْ تَتَوَضَّأْ وَقَدْ نِمْتَ فَقَالَ إِنَّمَا الْوُضُوءُ عَلَى مَنْ نَامَ مُضْطَجِعًا زَادَ عُثْمَانُ وَهَنَّادٌ فَإِنَّهُ إِذَا اضْطَجَعَ اسْتَرْخَتْ مَفَاصِلُهُ  

[Machine] I saw the Prophet ﷺ pray two rak'ahs before Fajr, then he slept until he snored and exhaled while he was prostrating or sitting. Then he stood up and prayed, so I said: O Messenger of Allah, you have slept. He said, "It is obligatory to perform ablution for the one who sleeps lying down, so when he lies down, his joints loosen."  

رَأَيْتُ النَّبِيَّ ﷺ صَلَّى رَكْعَتَيْنِ قَبْلَ الْفَجْرِ ثُمَّ نَامَ حَتَّى غَطَّ وَنَفَخَ وَهُوَ سَاجِدٌ أَوْ جَالِسٌ ثُمَّ قَامَ فَصَلَّى فَقُلْتُ يَا رَسُولَ اللهِ إِنَّكَ قَدْ نِمْتَ قَالَ «إِنَّمَا يَجِبُ الْوُضُوءُ عَلَى مَنْ نَامَ مُضْطَجِعًا فَإِذَا اضْطَجَعَ اسْتَرْخَتْ مَفَاصِلُهُ»  

"إِنَّ الوُضُوءَ لا يَجبُ إِلا على من نامَ مُضطجعًا، فإِنَّه إِذا اضطجعَ استرختْ مفاصِلُه .