Qualem commendes, etiam atque etiam aspice, ne mox incutiant aliena tibi peccata pudorem.
Look round and round the man you recommend,
For yours will be the shame should he offend.
Book I, epistle xviii, line 76 (translated by John Conington).
Variant translation: Study carefully the character of the one you recommend, lest his misdeeds bring you shame.