M. Tullius Cicero Divinatio in Q. Caecilium 62

[62] Wherefore, even if you could accuse him without violating strict right, still, as he had been in the place of a parent to you, you could not do so without violating every principle of piety. But as you have not received any injury, and would yet be creating danger for your praetor, you must admit that you are endeavouring to wage an unjust and impious war against him. In truth, your quaestorship is an argument of so strong a nature, that you would have to take a great deal of pains to find an excuse for accusing him to whom you had acted as quaestor, and can never be a reason why you should claim on that account to have the office of prosecuting him entrusted to you above all men. Nor indeed, did any one who had acted as quaestor to another, ever contest the point of being allowed to accuse him without being rejected.