It was narrated from 'Abdullah bin Buraidah that his father said: "The Messenger of Allah said: 'Whoever says: I have nothing to do with Islam, if he is lying then he is as he said, and if he is telling the truth, his Islam will not be sound'."
The Prophet Muhammad also taught us that lying is a sin, as it goes against the teachings of Islam which emphasize honesty and integrity. He was reminding us that if we make claims or statements which are untrue, then they will not be accepted by Allah or by other people who may hear them. Therefore, it is important for Muslims to always strive for truthfulness when speaking about their faith so that their words can be trusted by others around them.