Wudu before sleep
إِذَا أَتَيْتَ مَضْجَعَكَ فَتَوَضَّأْ وُضُوءَكَ لِلصَّلَاةِ، ثُمَّ اضْطَجِعْ عَلَى شِقِّكَ الْأَيْمَنِ
Idha atayta madja'aka fa-tawadda' wudu'aka li-s-salah, thumma-dtaji' 'ala shiqqika-l-ayman.
"When you go to your bed, perform wudu as you do for the prayer, then lie down on your right side."
Narrated by al-Bara' ibn 'Azib. Sahih al-Bukhari 247, Sahih Muslim 2710
A short reflection
The night begins clean and on the right side, and the du'a he taught next makes remembrance of Allah the last thing you say.