In the name of Allah, the Beneficent, the Merciful
Al-Nawawi records in his book Riyad us-Saliheen:
Al-Bara ibn Azib reported: The Messenger of Allah, peace and blessings be upon him, said:
إِذَا أَخَذْتَ مَضْجَعَكَ فَتَوَضَّأْ وُضُوءَكَ لِلصَّلاَةِ ثُمَّ اضْطَجِعْ عَلَى شِقِّكَ الأَيْمَنِ ثُمَّ قُلِ اللَّهُمَّ إِنِّي أَسْلَمْتُ وَجْهِي إِلَيْكَ وَفَوَّضْتُ أَمْرِي إِلَيْكَ وَأَلْجَأْتُ ظَهْرِي إِلَيْكَ رَغْبَةً وَرَهْبَةً إِلَيْكَ لاَ مَلْجَأَ وَلاَ مَنْجَا مِنْكَ إِلاَّ إِلَيْكَ آمَنْتُ بِكِتَابِكَ الَّذِي أَنْزَلْتَ وَبِنَبِيِّكَ الَّذِي أَرْسَلْتَ
When you go to bed, perform ablution as for prayer, then lie down on your right side and say: O Allah, I submit my face to You, and entrust my affair to You, and commit my back to You, out of hope and fear of You. There is no refuge or place of safety but with You. I believe in the Book that You have revealed, and the Prophet you have sent.
The Prophet said further:
وَاجْعَلْهُنَّ مِنْ آخِرِ كَلاَمِكَ فَإِنْ مُتَّ مِنْ لَيْلَتِكَ مُتَّ وَأَنْتَ عَلَى الْفِطْرَةِ
Make these your last words, for verily, whoever said this and died in the night will have died upon natural instinct.
Source: Sahih Muslim 2710, Grade: Sahih
Aisha reported:
كَانَ النَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ يُصَلِّي مِنْ اللَّيْلِ إِحْدَى عَشْرَةَ رَكْعَةً فَإِذَا طَلَعَ الْفَجْرُ صَلَّى رَكْعَتَيْنِ خَفِيفَتَيْنِ ثُمَّ اضْطَجَعَ عَلَى شِقِّهِ الْأَيْمَنِ حَتَّى يَجِيءَ الْمُؤَذِّنُ فَيُؤْذِنَهُ
The Prophet, peace and blessings be upon him, would pray eleven cycles (raka’ah) during the night, and when the dawn arrived he would pray two cycles. Then he would lie down on his right side until the caller to prayer would come to announce prayer.
Source: Sahih Bukhari 5951, Grade: Sahih
Abu Dharr reported: When the Messenger of Allah, peace and blessings be upon him, would go to sleep at night he would say:
بِاسْمِكَ نَمُوتُ وَنَحْيَا
In the name of Allah we die and we live.
When the Prophet woke up he would say:
الْحَمْدُ لِلَّهِ الَّذِي أَحْيَانَا بَعْدَ مَا أَمَاتَنَا وَإِلَيْهِ النُّشُورُ
All praise is due to Allah who has given us life after our death and to Him is the resurrection.
Source: Sahih Bukhari 6960, Grade: Sahih
Abu Ya’ish ibn Takhfah reported: On one occasion I was lying on my belly in the mosque when the Messenger of Allah, peace and blessings be upon him, shook me with his foot and he said:
إِنَّ هَذِهِ ضِجْعَةٌ يُبْغِضُهَا اللَّهُ
Verily, Allah disapproves of lying down like this.
Source: Sunan Abu Dawud 5040, Grade: Sahih
Abu Huraira reported: The Messenger of Allah, peace and blessings be upon him, said:
مَنْ قَعَدَ مَقْعَدًا لَمْ يَذْكُرْ اللَّهَ فِيهِ كَانَتْ عَلَيْهِ مِنْ اللَّهِ تِرَةٌ وَمَنْ اضْطَجَعَ مَضْجَعًا لَا يَذْكُرُ اللَّهَ فِيهِ كَانَتْ عَلَيْهِ مِنْ اللَّهِ تِرَةٌ
Whoever sits in a place and does not remember Allah will earn the displeasure of Allah, and whoever lies down for sleep and does not remember Allah will earn the displeasure of Allah.
Source: Sunan Abu Dawud 5040, Grade: Hasan
Abu Huraira reported: The Messenger of Allah, peace and blessings be upon him, said:
مَا مِنْ قَوْمٍ يَقُومُونَ مِنْ مَجْلِسٍ لاَ يَذْكُرُونَ اللَّهَ فِيهِ إِلاَّ قَامُوا عَنْ مِثْلِ جِيفَةِ حِمَارٍ وَكَانَ لَهُمْ حَسْرَةً
There are no people who rise from a gathering in which Allah was not mentioned but that it is as if they are rising from the carcass of a donkey, and it will be a cause of regret for them.
Source: Sunan Abu Dawud 4855, Grade: Sahih
Abu Huraira reported: The Messenger of Allah, peace and blessings be upon him, said:
مَا جَلَسَ قَوْمٌ مَجْلِسًا لَمْ يَذْكُرُوا اللَّهَ فِيهِ وَلَمْ يُصَلُّوا عَلَى نَبِيِّهِمْ إِلَّا كَانَ عَلَيْهِمْ تِرَةً فَإِنْ شَاءَ عَذَّبَهُمْ وَإِنْ شَاءَ غَفَرَ لَهُمْ
No people sit in a gathering without remembering Allah or sending blessings upon their Prophet except that they will earn the displeasure of Allah. If He wishes He will punish them, or if He wishes He will forgive them.
Source: Sunan At-Tirmidhi 3380, Grade: Sahih
Abbad ibn Tamim reported:
عَنْ عَمِّهِ أَنَّهُ رَأَى رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ مُسْتَلْقِيًا فِي الْمَسْجِدِ وَاضِعًا إِحْدَى رِجْلَيْهِ عَلَى الْأُخْرَى
His uncle saw the Messenger of Allah, peace and blessings be upon him, lying on his back in the mosque while placing one leg over the other.
Source: Sahih Bukhari 463, Grade: Sahih
Jabir ibn Samurah reported:
كَانَ النَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ إِذَا صَلَّى الْفَجْرَ تَرَبَّعَ فِي مَجْلِسِهِ حَتَّى تَطْلُعَ الشَّمْسُ حَسْنَاءَ
The Prophet, peace and blessings be upon him, would pray the dawn prayer and sit crossed legged in his place until the sun had risen brightly.
Source: Sunan Abu Dawud 4850, Grade: Sahih
Ibn Umar reported:
رَأَيْتُ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ بِفِنَاءِ الْكَعْبَةِ مُحْتَبِيًا بِيَدِهِ هَكَذَا
I saw the Messenger of Allah, peace and blessings be upon him, sitting by the Ka’bah with his thighs on his stomach and arms around his legs.
Source: Sahih Bukhari 5917, Grade: Sahih
Qaylah bint Makhramah reported:
أَنَّهَا رَأَتْ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ وَهُوَ قَاعِدٌ الْقُرْفُصَاءَ فَلَمَّا رَأَيْتُ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ الْمُخْتَشِعَ
She saw the Prophet, peace and blessings be upon him, sitting with his arms around his legs. She said: When I saw the Messenger of Allah in such a humble position I was overcome with awe.
Source: Sunan Abu Dawud 4847, Grade: Hasan
Shareed ibn Suwaid reported: The Messenger of Allah, peace and blessings be upon him, passed by me while I was sitting with my left hand behind my back and leaning upon it. The Prophet said:
أَتَقْعُدُ قِعْدَةَ الْمَغْضُوبِ عَلَيْهِمْ
Do you sit like one with whom Allah is angry?
Source: Sunan Abu Dawud 4848, Grade: Sahih
Success comes from Allah, and Allah knows best.