Therefore...
Therefore, there is no problem that Qur'an has expressed only a part of cases of Khums and has leaved the others to tradition, and there are lots of issues like this in Islamic Fiqh and those who know even a little about issue of Fiqh have understood this matter completely; but we should find that what the meaning of advantage (غنيمت) literally and in commonsense is. Indeed, is it exclusive to spoils of war or it consists of any kind of income?
و فى الحديث الرّهن لمن رهنه له غنمه و عليه غرمه، غنمه زيادته و نمائه و فاضل قيمته... و غنم الشّىء غنما: فاز به “غنم” means gaining a thing without any hardship and “غنم”, “غنيمت” (advantage) and “مغنم” are all in the meaning of “فيء” (and also “فيء” has been meant literally as the things which reach a person without labor …) and it has been said in Hadith that pawn is for the person who has taken that pawn and its advantage (غنيمت) and benefit is for him, and also its compensation and loss is for him, and “غنم” means the excess, growth and surplus of the price … he take that as an advantage (غنيمت) means that he gained that … And we read in the book “Taj Al-Arous” (the bride’s brown), vol.
9: والغنم الفوز بالشيء بلا مشقّة! Advantage (غنيمت) is the thing that person gains without hardship! And also in the book “Al-Qamoos” it has been mentioned with the same meaning. And in the book “Mufradat” by Ragheb “غنيمت” has been said to be derived from the root “غنم” in the meaning of “sheep” and then it says: ثم استعمل فى كل مظفور به من جهة العدى و غيرهم Then it has been used in all things which person gains from enemy or non-enemy.
Even persons who consider one of the definitions of “غنيمت” as spoils of war do not deny that its main meaning is more expanded which implies to all things that a person can gain without hardship. In common use advantage “غنيمت” is used against Fine “غرامت” and as the meaning of fine is an expanded meaning and consists of any kind of fine, also advantage “غنيمت” has an expanded meaning and implies to any kind of notable income.