The shifts of Fortune test the reliability of friends.
Cicero (106 BC - 43 BC), De Amicitia
Have no friends not equal to yourself.
Confucius (551 BC - 479 BC), The Confucian Analects
Be courteous to all, but intimate with few, and let those few be well tried before you give them your confidence. True friendship is a plant of slow growth, and must undergo and withstand the shocks of adversity before it is entitled to the appellation.
George Washington (1732 - 1799)
In prosperity our friends know us; in adversity we know our friends.
John Churton Collins