Khums is one of the pillars of Islam which was ordained by Allah and practiced during the life of the Messenger of Allah. Khums means “one-fifth,” and indicates that one fifth of a person’s excess income has to be dedicated, according to the Qur’an, for the following,
“And know that whatever profit you make, verily, one-fifth of it is assigned to Allah and to the Messenger and to his family and also the orphans, the destitute, and the wayfarer, if you have believed in Allah, and in that which We sent down to our servant Muhammad.”
Khums, in brief, means paying one-fifth of the surplus of one’s income after taking away the expenses of the person and his dependants. It consists of two equal parts: one being the share of the Imam, meaning that this part goes for constructing masjids, Islamic seminaries, Islamic schools, libraries, hospitals or clinics, orphanages, printing of the Noble Qur’an, hadith books, Islamic books and lectures, and others things which will benefit, defend, or propagate Islam. The second part is the portion for the poor sayyids (descendants of the Prophet), since they are banned from receiving zakat (charity).
Many historical references from different schools of thought mention that the khums existed during the time of the Prophet and was banned during the time of the first and second caliphs. The interpretation by the Ahlul Bayt of the word “ghanimtum” in the Qur’an, chapter 8, verse 41 is “everything you gained”—whether from war, work, trade, or other sources, since Islam’s history testifies that the Prophet took out one-fifth from the war booty, and also from assets other than the war booty during peacetime. Other non-Shi‘a scholars have supported this position.
 Noble Quran, 8:41
 Sunan al-Bayhaqi, Vol. 6, “Sahm Dhil Qurba”; Musnad al-Shafi‘i, “al-Fay’”, 187; Sunan Abu Dawud, Vol. 18, “al-Khums”; Musnad Ahmad ibn Hanbal, Vol. 1, 320; al-Muttaqi al-Hindi, Kanz al-Ummal, Vol. 2, 305; Lisan al-Mizan, Vol. 6, 148; Huliyat Abu Nu‘aym, Vol. 2, 205; Sahih Muslim, Vol. 5, 198; Sunan al-Nisa’i, 177 and 178; Tafsir al-Tabari, Vol. 10, 5
 See for further details: Musnad Ahmad ibn Hanbal, Vol. 1, 314; Sunan ibn Majah, 839
 Al-Qadi Abu Yusuf, Kitab al-Kharaj, 25-27