The names of Allah (the Asma ul-Husna) fall into two categories.
1) Names that refer exclusively to Allah's essence, or that are used solely to express attributes that belong to Allah alone. It is not permissible under any circumstances to use these names for anyone other than Allah. Examples include: Allah, Ar-Rahman, Al-Quddus, Al-Jabbar, Al-Mutakabbir, Al-Khaliq, Al-Bari, Al-Musawwir, Al-Ghaffar, Al-Qahhar, At-Tawwab, Al-Wahhab, Al-Khallaq, Ar-Razzaq, Al-Fattah, Al-Qayyum, Ar-Rabb, Al-Muhit, Al-Malik, Al-Ghafur, Al-Ahad, As-Samad, Al-Haqq, Al-Qadir, Al-Muhyi, and others.
For any of these names to be used for a person, the word "Abd" must be added at the beginning. Using them without "Abd" is not permissible.
2) Names that are not exclusive to Allah's attributes but are used to describe both Allah and others as well. These are known as shared attributes (sifat mushtarakah). Regarding these, the detail is as follows: if it is established from the Quran, hadith, the practice of the Ummah, or common usage that such a name has been given to someone other than Allah, then there is no objection to using it as a name. Examples include: Aziz, Ali, Karim, Rahim, Azeem, Rashid, Kabir, Badi, Kafil, Hadi, Wasi, Hakim, and others.
However, where there is no established precedent in the Quran, hadith, or the practice of the Ummah for using a shared attribute as a name for someone other than Allah, it should be avoided. If one still wishes to use it, "Abd" should be added at the beginning, because the default principle regarding the Asma ul-Husna is that using them as names for anyone other than Allah is not permissible.
In light of the above, the ruling for the case in question is that instead of using "Hanan" (حنان) alone, the name "Abd ul-Hanan" (عبد الحنان) is more appropriate.
(Derived from Fatawa Uthmani, Vol. 1, p. 50, Maktabah Ma'arif ul-Quran)
Allah the Almighty knows best.
Darul Ifta Al-Ikhlas, Karachi.