משנה על גיטין 2:1

He also testified concerning a small village in the vicinity of Jerusalem in which there was an old man who used to lend to all the people of the village and write out [the bond] in his own handwriting and others signed it. And when the fact was brought before the Sages they pronounced it legal. Hence, incidentally, you may infer that a wife may write her own bill of divorcement, and a husband may write his own receipt; for the legality of a document depends only on those who sign it. And [he testified] concerning a needle which was found in flesh of a [sacrifice], that the knife and the hands [which had been employed on the flesh] are clean, but the flesh itself is defiled; and if it was found in the excrement, all are clean.