It is narrated from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "Keep regard for me concerning the Arabs, for three qualities: because I am an Arab, the Qur'an is in Arabic, and the language of the people of Paradise is Arabic." Imam al-Hakim says: The narration of Yahya bin Burayd from Ibn Jurayj is sahih; I have mentioned the narration of Muhammad bin al-Fadl in support of it. Whoever takes lightly this saying of the Prophet (peace and blessings be upon him), "The language of the people of Paradise is Arabic," is falling short in regard to Allah and His Messenger, for its supporting reports contain a severe warning for those who prefer Persian over Arabic in speaking or writing. Further hadiths on this subject have also reached us, some of which are these:

It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever among you is able to speak Arabic should never speak in Persian, for it breeds hypocrisy."

It is narrated from Sayyiduna Anas bin Malik (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever speaks in Persian, his cunning increases and his muru'ah (manliness) decreases."