Al-Ashtar (Malik bin al-Harith al-Ashtar, may Allah have mercy on him) said: There was some exchange of words between Sayyiduna Ammar and Sayyiduna Khalid bin al-Walid (may Allah be pleased with them both), and Khalid bin al-Walid (may Allah be pleased with him) complained about it to the Prophet (peace and blessings be upon him). The Messenger of Allah (peace and blessings be upon him) said: "Whoever shows enmity to Ammar, Allah will show enmity to him, and whoever calls Ammar foolish, Allah will declare him foolish." (The narrator Shu'bah said: Salamah also narrated something similar.)
Hadith Referenceالمعجم الكبير للطبراني / باب الخاء / 3816