Sahih Bukhari Volume 007, Book 062, Hadith Number 062.
Narrated By 'Aisha : (Regarding His Statement): 'They ask your instruction concerning the women. Say: Allah instructs you about them...' (4.127) It is about the female orphan who is under the guardianship of a man with whom she shares her property and he does not want to marry her and dislikes that someone else should marry her, lest he should share the property with him, so he prevents her from marrying. So Allah forbade such a guardian to do so (i.e. to prevent her from marrying).