Trim mustaches and let beards grow accordingto instructions given by Prophet Muhammed PBUH .

According to the hadith narrated by Ibn 'Umar, the Prophet Muhammad (PBUH) instructed Muslims to trim their mustaches and let their beards grow. This is a practice that has been followed by many Muslims throughout history as a sign of piety and respect for Islamic teachings. It is important to note that this practice is not mandatory, but rather it is recommended as a way of showing respect for Islamic teachings. Additionally, it serves as an outward sign of one's commitment to following the Sunnah of the Prophet Muhammad (PBUH). By following this Sunnah, one can demonstrate his or her dedication to living according to Islamic principles.

The act of trimming one's mustache and letting one's beard grow also serves as an outward symbol of modesty in accordance with Islamic teachings. It helps keep facial hair neat while still allowing it to remain visible enough so that others can recognize its presence on someone’s face. This helps promote modesty among Muslim men who are expected not only dress modestly but also groom themselves in such a way that reflects their commitment towards living according to Islamic principles.