One should make wudhu before going to sleep
عن البراء بن عازب رضي الله عنهما قال قال لي رسول الله صلى الله عليه وسلم إذا أتيت مضجعك فتوضأ وضوءك للصلاة (بخاري رقم 247)
Hadhrat Baraa bin Aazib (Radhiyallahu Anhu) reports that Rasulullah (Sallallahu Alaihi Wasallam) advised him: “When you are retiring to bed, then perform wudhu as you perform wudhu for salaah.”