Musannaf Ibn Abi Shaybah

Hazrat Umar bin Zaid narrates that Hazrat Umar wrote a letter to Hazrat Abu Musa Ash'ari and said: After praise and salutations. So, develop understanding in the Sunnah, and develop understanding in the Arabic language, and recite the Qur'an by clarifying its diacritical marks. Because it is in the Arabic language, and attribute yourselves to the tribe of Ma'ad, because you are from the people of the tribe of Ma'ad.