From Sahih Bukhari (Hadith 5131):
Narrated `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)
Reference: Bukhari 5131