Surah 4. An-Nisaa', Ayah 4

The expression nihlah signifies the giving of something willingly, of one's own accord, without expecting a return for it (Zamakhshari). It is to be noted that the amount of the marriage-portion, or dower, which the bridegroom has to give to the bride has not been circumscribed by the Law: it depends entirely on the agreement of the two parties, and may consist of anything, even a mere token. According to several authentic Traditions recorded in most of the compilations, the Prophet made it clear that "even an iron ring" may be enough if the bride is willing to accept it, or, short of that, even "the imparting to thy bride of a verse of the Qur'an".