Ibn 'Umar (May Allah be pleased with them) reported: The Prophet ﷺ as saying: "The worst of lies is to pretend to have seen something which he has not seen". Al- Bukhari.
The Prophet Muhammad (peace be upon him) was known for his honesty and truthfulness throughout his life, so it makes sense that he would emphasize this point in a hadith. He wanted us to understand how important it was for us to remain truthful at all times, no matter what situation we find ourselves in or what temptations may come our way. By following this advice from the Prophet Muhammad (peace be upon him), we can ensure that we stay on the path towards righteousness and gain Allah's pleasure through our words and deeds.