Buraydah (may Allah be pleased with him) reported that the Messenger (may Allah's peace and blessings be upon him) said: "Do not call a hypocrite a master, for if he is a master, you will have angered your Almighty Lord."
Meaning of the Hadīth: If a hypocrite is a master among his people and you call him as such, you will incur the wrath of Allah, as you revere that hypocrite who does not deserve such treatment; and if he is not a master or leader, you will be lying and flattering. So, in both cases, he forbids us from addressing a hypocrite as master, with the same applying to a disbeliever, a defiantly disobedient Muslim, or a heretic, for they do not deserve this title at all. The prohibition was addressed to the Companions and those who came after them. Hypocrites at the time were of two types: First: Hypocrites known only to the Prophet (may Allah's peace and blessings be upon him) and his confidant Hudhayfah (may Allah be pleased with him). Second: Hypocrites known among the Companions for their hypocrisy, such as ‘Abdullāh ibn Ubayy. Those fall under the ruling stated in the Hadīth.