Sirach 6:7-9

Revised Standard Version

⁷ When you gain a friend, gain him through testing,
    and do not trust him hastily.
⁸ For there is a friend who is such at his own convenience,
    but will not stand by you in your day of trouble.
⁹ And there is a friend who changes into an enemy,
    and will disclose a quarrel to your disgrace.