One-fifth is mentioned in the Quran in these verses:

[8:41] You should know that if you gain any spoils in war, one-fifth shall go to God and the messenger, to be given to the relatives, the orphans, the poor, and the traveling alien. You will do this if you believe in God and in what we revealed to our servant on the day of decision, the day the two armies clashed. God is Omnipotent.

To learn more, read the Quran in English.

Want to study the Quran every week? We provide online Friday meetings every Friday.