That we must not labour noisily nor boastfully
In the Gospel according to Matthew: “Let not your left hand know what your right hand does, that your alms may be in secret; and your Father, which sees in secret, shall render to you.” Also in the same place: “When you do an alms, do not sound a trumpet before you, as the hypocrites do in the streets and in the synagogues, that they may be glorified of men. Verily I say unto you, They have fulfilled their reward.”
Source: The Treatises of Cyprian (New Advent)