Narrated Az-Zuhri:Urwa bin Az-Zubair said that he asked 'Aisha about the meaning of the Quranic Verse:--
"And if you fear that you will not deal fairly with the orphan girls then marry (other) women of your choice." (4.2-3)
Aisha said, "It is about a female orphan under the guardianship of her guardian who is inclined towards her because of her beauty and wealth, and likes to marry her with a Mahr less than what is given to women of her standard. So they (i.e. guardians) were forbidden to marry the orphans unless they paid them a full appropriate Mahr (otherwise) they were ordered to marry other women instead of them. Later on the people asked Allah's Apostle about it. So Allah revealed the following Verse:--
"They ask your instruction (O Muhammad!) regarding women. Say: Allah instructs you regarding them..." (4.127)
and in this Verse Allah indicated that if the orphan girl was beautiful and wealthy, her guardian would have the desire to marry her without giving her an appropriate Mahr equal to what her peers could get, but if she was undesirable for lack of beauty or wealth, then he would not marry her, but seek to marry some other woman instead of her. So, since he did not marry her when he had no inclination towards her, he had not the right to marry her when he had an interest in her, unless he treated her justly by giving her a full Mahr and securing all her rights.