John Cassian, The Institutes IX.10: Of the only thing in which dejection is useful to us

And so we must see that dejection is only useful to us in one case, when we yield to it either in penitence for sin, or through being inflamed with the desire of perfection, or the contemplation of future blessedness. And of this the blessed Apostle says: “The sorrow which is according to God worketh repentance steadfast unto salvation: but the sorrow of the world worketh death.”