Invocation is permissible at all times and purification is not one of its conditions

[Amar.Abu.Yahia]

Q: Is it permissible to invoke Allah outside Salah (Prayer) times while a person has not performed Wudu' (ablution) such as at work; shall he be answered in this condition?

A: Invocation is permissible at all times and purification is not one of its conditions. A person may invoke Allah in all circumstances whether he is ritually pure, in the state of Janabah (major ritual impurity related to sexual discharge), or has not performed Wudu' (ablution) or if a woman is in her menses or in post-childbirth. Invocation is required as well as Dhikr Remembrance of Allah). From the types of Dhikr are the following: Subhana Allah Wal-Hamdu Lillah Wla Ilaha Illa Allah Wa Allahu Akbr (Glorified be Allah, Praise be to Allah, there is no god but Allah and Allah is the Greatest!). A person may perform Dhikr in all cases, even a woman in her period or post-childbirth and the one in the state of Janabah. Lady `Aishah (may Allah be pleased with her) said: The Prophet (peace be upon him) used to remember Allah at all times. Verily! In the creation of the heavens and the earth, and in the alternation of night and day, there are indeed signs for men of understanding. Allah (Glorified and Exalted be He) says: Those who remember Allâh (always, and in prayers) standing, sitting, and lying down on their sides

A believer is permitted to perform Dhikr in all cases but a person is forbidden to recite the Glorious Qur'an, in particular, in the state of Janabah. Allah (may He be Praised and Glorified) says: Then when the (Jumu‘ah) Salât (prayer) is ended, you may disperse through the land, and seek the Bounty of Allâh (by working, etc.), and remember Allâh much: that you may be successful.

A believer is always required to perform Dhikr; whether standing, sitting or when lying on his side in all cases except for reciting the Qur'an during which he must be pure from Janabah.

Source:
http://alifta.com/Fatawa/FatawaChapt...No=1&BookID=14