Wiktionary
take the pledge
vb. (context US dated English) To promise to abstain from alcohol.
Usage examples of "take the pledge".
He stood with the seven newly chosen Great Ones ready to take the pledge of fealty.
Valla was dozing, and the brandy bottle was half-empty - if ever they start the Little White Ribboners in Russia, all the members will have to be boys, for they'll never get the women to take the pledge.
It crossed her mind to take the pledge, go on the wagon, but she couldn't decide which was worse: pending alcoholism, or remorseless unrelenting sobriety of the rest of her days.