(in the pure Tradition of the Prophet pbuh)
This wudhuu’ is not obligatory, but is very highly and definitely commendable. This (i.e. its not being obligatory) is based on the hadith narrated by ‘Umar (rad) in which he asked the Prophet (pbuh): “Should we go to sleep in a state of janaba?” To which the Prophet (pbuh) answered: “Yes, and perform wudhuu’ if you wish.” [Ibn Hibbaan: Saheeh]. This is also supported by other hadith, among them a hadith narrated by ‘Aa’ishah (rada)who said: “The Prophet (pbuh) used to sleep in a state of janaba without having touched water, until he would get up later and bathe.” [Ibn Abi Shaiba, at-Tirmidhee, Abu Daawood and others: Saheeh].
In another version narrated by ‘Aa’ishah (rada), she said: “”He used to spend the night in a state of janaba until Bilal (rad) came in the morning to make the adhaan. Then, he would get up, bathe while I looked at the water dripping from his head, and go out. Then, I would hear his voice in the Fajr prayer. Then, he would remain fasting.” Mutarrif said: “I said to Aamir: In the month of Ramadhaan?” He said: “Yes, in Ramadhaan and in other than Ramadhaan.”” [Ibn Abi Shaiba, Ahmad and others: Saheeh].