Wa `alaykum As-Salamu wa Rahmatullahi wa Barakatuh.

Masturbation is human practice to bring relief from sexual needs that can visit the body every often. Although there is no direct verse of Hadith that speaks directly about the prohibition of it but there is a consensus among scholars that it is not permissible and haram except for Imam Ahmad in one of his views as he considered it permissible.

My advice for you is to have faith in yourself and to start slowing down on it. The much practice of it will make it an addiction that even with marriage later it will be the dominant way of sexual relief instead of the natural intercourse with a wife.

I have had women come and complain about husbands that they relief themselves even after marriage in this way and have not much interest in intercourse which is a right of a woman in marriage.

I am not expecting that you can totally be out from it, so take it easy on yourself and do not keep looking down at yourself. Avoid things that will prompt you to keep practicing it many times, keep busy, practice athletic activities. I lean to the view that a person can practice it only if he fears for adultery or Zina on himself and in the minimum number of times not the continuous addictive way.