Sayyiduna Zayd bin Thabit (may Allah be pleased with him) narrates: the Messenger of Allah (peace and blessings be upon him) ordered me to learn the writing of the Jews, and not even half a month had passed before I became proficient in it. the Messenger of Allah (peace and blessings be upon him) said: "I do not trust the Jews with my writing." When I had learned it, I began writing letters for him (peace and blessings be upon him).
Hadith Referenceالمعجم الكبير للطبراني / باب الزاي / 4838