It is a recommended Sunnah to sleep in a state of ritual purity.
[Shurunbulali, Maraqi al-Falah]
There are 5 benefits of sleeping with Wudhoo:
- Angels would pray for you (make dua)
The Messenger of Allah (Allah bless him and give him peace) said,
“When you go to bed, you should perform the ablution (wudu) for the prayer, and then lay down on your right side. Then say, ‘O Allah, I have turned my face to You and I have surrendered my self to You and I have committed my back to You out of fear and desire for You. There is no place of safety or refuge from You except with You. I have believed in Your book which You revealed and Your Prophet whom You sent.’ If you die that night, you will die in fitra (natural state). And make these the last words you utter.'” [Bukhari]
This means that the angels will pray for you.
As for the angels praying for you, this too has been related. It is reported that the Messenger of Allah (Allah bless him and give him peace) said,
“Purify these bodies, and Allah will purify you. There is not a slave who spends his night in a state of purification except that an angel spends the night besides him. And whenever the slave turns over during the night, the angel says: ‘O Allah, forgive Your slave, for he went to sleep in a state of purification.’” [Tabarani, al-Mu`jam al-Kabir], (Al-Mu’jamul Awsat of Tabarani, Hadith: 5087)
- The soul will make sajdah under the ‘Arsh (Throne) of Allah Most High.
Sayyiduna Abud Darda (radiyallahu ’anhu) has said:
‘When a person sleeps, his soul (ruh) rises to the throne (‘Arsh) of Allah. If he slept with wudu, the soul is permitted to make sajdah (by the ‘Arsh of Allah). If he slept in the state of impurity, permission for sajdah is refused.’
(Kitabuz Zud of Ibnul Mubarak, Hadith: 1245. Also see: Fathul Bari, Hadith: 1149)
- The reward of engaging in salah and dhikr the entire night.
Imam Abu Murayah Al ‘Ijli (Allah’s mercy be upon him) said:
‘Whoever retires to bed in the state of wudu and falls off to sleep while engaging in the dhikr of Allah Most High, his bed will be regarded as a Masjid. He will receive the reward of being in salah and dhikr until he awakens.’
The narration is suitable to quote as reported.
(Musannaf ‘Abdur Razzaq, Hadith: 19837 and Fathul Bari, Hadith: 6311)
- Be raised on the day of Qiyamah with Wudu
The ‘Ulama state that one of the primary reasons for sleeping with wudu is to prepare for death.
Sayyiduna Ibn ‘Abbas (Allah be pleased with them) advised:
‘Ensure that you spend the nights in wudu, for the souls will be raised in the condition [of purity] that they were taken in.’
(Musannaf ‘Abdur Razzaq, see Fathul Bari, Hadith: 6312 and ‘Umdatul Qari, Hadith: 247)
- Protection from nightmares
Hafiz Ibn Hajar (Allah’s mercy be upon him) writes:
‘One who sleeps with wudu will see better dreams.’
(Fathul Bari, Hadith: 6311)
Shaykhul Hadith Moulana Muhammad Zakariyya Kandehlawi (Allah’s mercy be upon him) says:
‘One who sleeps with wudu is saved from bad dreams.’
(Taqrir Bukhari 2/78)
To summarise, the following benefits of sleeping with wudhoo are:
- Angels making dua for you
- The soul will make sajdah under the ‘Arsh (Throne) of Allah Most High
- The reward of engaging in salah and dhikr the entire night
- Be raised on the day of Qiyamah with Wudu
- Protection from nightmares
And Allah knows best.
Source: MuslimVillage.com