Verse 4 says that the believers pay "Zakat", i.e. poor-due that is paid on one's wealth. Commentators on the Qur'an, like Ibn Kathir are of the opinion that this verse could also be referring to the poor-due mentioned in Sura 6:141 which states ""pay the due thereof on the day of their harvest."", as well as that it could be that what is meant here by Zakaat is purification of the soul from Shirk and filth, as in Sura 91:9-10 which says ""Indeed he succeeds who purifies himself (Zakkaha). And indeed he fails who corrupts himself."" The commentators are hence of the opinion that probably both meanings are intended, purification of the soul as well as purification of one's wealth, because that is also part of the purification of the soul, and the true believer is one who pays attention to both matters.