Midrash su Salmi 39:2

Mar Ukba sent the following message to R. Elazar: "What is the statute concerning people who arise against me, against whom I have the power to give over [as captives] to the government: [may I do it or no?"] Whereupon the latter wrote to him in underlined form the following passage (Ps. 39, 2) I said I will take heed to my ways that I sin not with my tongue: I will keep a curb upon my mouth, while the wicked is before me: i.e., although the wicked is against me vet will I keep a curb upon my mouth." The former again sent to him: "They are troubling me exceedingly so that I cannot stand, because of it." R. Elazar then sent him word (Ib. 37, 7) Be silent before the Lord and He will cause them to fall before thee as victims. Arise early and remain late in spite of them in the house of study, and they shall cease [to exist of themselves]." When this message went forth from R. Elazar's mouth, the consequence was that [Gniba], the opponent of Mar Ukba, was put in chains, [upon charges brought against him by the Roman Government.]