It is permissible for a person, if he is junub, to make du’aa’ to Allaah and remember Him, including the adhkaar before sleeping and others, because of what is reported in the hadeeth of ‘Aa’ishah (may Allaah be pleased with her), who said, “The Messenger of Allaah (peace and blessings of Allaah be upon him) used to remember Allaah in all circumstances.” (Narrated by Muslim, al-Hayd, 558). Some of the commentators on this hadeeth said: this hadeeth is stating a basic principle, which is the remembrance of Allaah in all circumstances, even when one is in a state of minor or major impurity. Dhikr in the form of tasbeeh (saying ‘Subhaan Allaah’), tahleel (saying ‘Laa ilaaha ill-Allaah’), takbeer (saying ‘Allaahu akbar’), tahmeed (saying ‘al-hamdu Lillaah’) and other similar adhkaar is permissible in all situations, according to the consensus of the Muslims. What is forbidden is dhikr that consists of reciting Qur’aan, a full aayah or more, whether that is read from the Mus-haf or recited by heart, because the prohibition of doing so has been narrated. But it is mustahabb for the person who is junub to wash his private parts and do wudoo’ when he wants to go to sleep, because of what is stated in the hadeeth of ‘Umar (may Allaah be pleased with him), who said, “O Messenger of Allaah, may one of us sleep when he is junub?” He said, “Yes, if he does wudoo’.” (Narrated by al-Bukhaari, al-Ghusl, 280) 

See al-Sharh al-Mumti’ by Ibn ‘Uthaymeen, 1/288; Tawdeeh Ahkaam by al-Bassaam, 1/250; Fataawa Islamiyyah, 1/232