It is narrated from Sayyiduna Zayd bin Thabit (may Allah be pleased with him); he said that the Messenger of Allah (peace and blessings be upon him) said: "Letters come to me from people, and I do not want just anyone to read them. So can you learn the Syriac language?" I said: "Yes." (Sayyiduna Zayd (may Allah be pleased with him) said:) So I learned the language in seventeen (days).
Hadith Referenceالمعجم الكبير للطبراني / باب الزاي / 4908