Inscribe a binding circle upon the ground or floor; it should be a circle containing a hexagram, with the symbols of the four elements and the Sun and Moon in each corner, along with a symbol of the deity you work with in the center. Have a candle, a pinch of salt, a container of water, and a burning censer at each one of the four points of the circle.
Now, if for some horrible reason you summon a malevolent spirit, immediately repeat this spell:
Vi ignis obligo tibi.
Vi aquae obligo tibi.
Vi terra tibi obligo.
Vi aeris obligo tibi.
Vi solis ac lunae obligo tibi.
In nomine Dei /dea Iubeo te! Ut Ignis vinculis constringo vos. In carcere aquae, exorcizo te. Ego incarcerare vos in visceribus terrae. Ego caperent vos in compedibus Aeris. Et humilia te sub lumina solis et lunae. In nomine Dei /dea circuli obligo vos, spiritus immunde, ut nihil mali faciatis.
I bind you the power of the fire.
I bind you by the power of water.
I bind you by the power of the earth.
I bind you by the power of air.
I bind you by the power of the sun and of the moon.
In the name of the God/goddess (insert name here), I command you! May chains of Fire bind you. I cast thee into a prison of Water. I imprison you in the bowels of the earth. I entrap you in the air with chains. Humble yourself under the lights of the sun and of the moon. In the name of the God/goddess of the circle, I bind you, unclean spirit, in order that ye do no evil!
If this works, the spirit will be trapped in the circle unless it is either broken or the spirit is successfully banished later; hopefully the latter. Use at your own risk.