“If you want to fast according to Christ and to humble your soul, every time of the entire year is open to you; moreover, hold all the days of your life for humbling your soul, if you have learned from the Lord our Savior that he is gentle and lowly in heart (Matt 11:29). When, therefore is there not a day of humiliation for you who follow Christ who is lowly in heart and a teacher of humility?”
Origen of Alexandria (182-254), Christian theologian and Church Father, in Homilies on Leviticus 10.3.