If thou wouldst get a friend, prove him first, and be not hasty to credit him. For some man is a friend for his own occasion, and will not abide in the day of trouble.

Ecclesiasticus

When I see leaves drop from their trees in the beginning of autumn, just such, think I, is the friendship of the world. Whilst the sap of maintenance lasts, my friends swarm in abundance; but in the winter of my need they leave me naked. He is a happy man that hath a true friend at his need; but he is more truly happy that hath no need of his friend.

Warwick

As the yellow gold is tried in the fire, so the faith of friendship must be seen in adversity.

Ovid

True friendship, like a star, is made brilliant by the dark night.

Anon