DEMANDING DOWRY IN MARRIAGE

Believer to beg from somebody without a stringent, pressing need.  There are warnings in the Hadith about this:

Translation of Hadith:  There is a very lengthy Hadith narrated on the authority of Hadhrat Habshi Bin Janadah As Saluli in which the Holy Prophet (Sallallahu alaihi wa sallam) said: Begging is not permissible for some who is wealthy and someone with a sound body, excepting for someone who is very poor and someone in a very great need.  If a person begs to increase wealth, then in Qiyamah, that begging will be on his face in the form of scratches and it will come in the form of an ember, from which that person will eat.  Whoever wants to can decrease or increase this punishment for himself.

(Jame' Tirmidhi, Kitab Uz Zakaah, Vol. 1, Pg No. 141, Hadith No: 590)

However, without any demand of any kind, exchanging gifts willingly is allowed.  Islam has declared exchange of gifts to be a means of maintaining and increasing love, as the Holy Prophet (Sallallahu alaihi wa sallam) said in (Kanz Ul Ummal, Hadith No: 15057).  Thus, giving a gift on the occasion of marriage is permissible.