“Therefore, it is necessary that infidelity should be cursed in order to serve the faith (Islam). Cursing unbelief in the heart is the lesser way. The greater way is to curse it in the heart as well as with the body. In short, cursing means to nourish enmity towards enemies of the true faith, whether that enmity is harboured in the heart when there is fear of injury from them (infidels), or it is harboured in the heart as well as served with the body when there is no fear of injury from them.
In the opinion of this recluse, there is no greater way to obtain the blessings of Allah than to curse the enemies of the faith (be impatient with them). For Allah himself harbours enmity towards the infidels and infidelity…
Once I went to visit a sick man who was close to death. When I meditated on him, I saw that his heart was layered with darknesses. I intended to remove those darknesses. But he was not yet ready for it… When I meditated more deeply, I discovered that those darknesses had gathered due to his friendship with the infidels. They could not be dispersed easily. He had to suffer torments of hell before he could get purged of them…”

Source: The Seth Material (1970), p. 274
Context: It is wrong to curse a flower and wrong to curse a man. It is wrong not to hold any man in honor, and it is wrong to ridicule any man. You must honor yourselves and see within yourselves the spirit of eternal vitality. If you do not do this, then you destroy what you touch. And you must honor each other individual also, because in him is the spark of eternal vitality. When you curse another, you curse yourselves, and the curse returns to you. When you are violent, the violence returns... I speak to you because yours is the opportunity [to better world conditions] and yours is the time. Do not fall into the old ways that will lead you precisely into the world that you fear.

Source: Gaudy Night

This exact expression has not been located in available editions of this work, and might be simply a paraphrase of the above statement.
Variant: To teach is to touch the heart and impel it to action.
Source: Kindergarten Chats (1918), Ch. 36 : Another City

Variant: A Very Short Song

Once, when I was young and true,
Someone left me sad-
Broke my brittle heart in two;
And that is very bad.

Love is for unlucky folk,
Love is but a curse.
Once there was a heart I broke;
And that, I think, is worse.
Source: Enough Rope

Sia maladetto chi si fidò mai,
O vuol fidarsi di donna che sia;
Che false sono e maladette tutte;
E più anche le belle che le brutte.
XXII, 49
Rifacimento of Orlando Innamorato

Source: The Curse of Chalion

Speaking in elegy regarding the recent death of Michael Collins. From " Poblacht na-Eireann (War News ) No. 47 " Thursday 24 August 1922.
Literary Years and War (1900-1918), Last Years: Ireland (1919-1922)

John Knox as portrayed in Bothwell : A Tragedy (1874) Act I, Sc. 2.
Bothwell : A Tragedy (1874)
Context: Sins are sin-begotten, and their seed
Bred of itself and singly procreative;
Nor is God served with setting this to this
For evil evidence of several shame,
That one may say, Lo now! so many are they;
But if one, seeing with God-illumined eyes
In his full face the encountering face of sin,
Smite once the one high-fronted head, and slay,
His will we call good service. For myself,
If ye will make a counsellor of me,
I bid you set your hearts against one thing
To burn it up, and keep your hearts on fire,
Not seeking here a sign and there a sign,
Nor curious of all casual sufferances,
But steadfast to the undoing of that thing done
Whereof ye know the being, however it be,
And all the doing abominable of God.
Who questions with a snake if the snake sting?
Who reasons of the lightning if it burn?
While these things are, deadly will these things be;
And so the curse that comes of cursed faith.

Source: Nothing Like the Sun