Will a person be punished for abandoning the Prophetic Sunnahs, such as letting the izar hang low (isbal), shaving the beard, and not trimming the mustache, and what are the consequences of that?

It is not characteristic of a Muslim to turn away from the Sunnah of the Prophet (peace be upon him), for the Prophet (peace be upon him) said: "Whoever turns away from my Sunnah is not of me." Allah Almighty has linked obedience to Him with obedience to His Messenger, and made following the Prophet a sign of Allah's love. Obedience is a cause for entering Paradise, and disobeying the Prophet's command (peace be upon him) is a cause for discord and a painful punishment.

Regarding isbal (letting one's garment hang below the ankles), the Prophet (peace be upon him) strictly forbade it. It is narrated in Sahih Muslim that "There are three types of people whom Allah will not speak to on the Day of Resurrection, nor look at them, nor purify them, and they will have a severe punishment," and among them he mentioned "the one who lets his garment hang low." The Prophet (peace be upon him) specified that the believer's izaar (lower garment) should be "up to the middle of his shins, then to his ankles. Whatever is below that is in the Fire."

As for shaving the beard and not trimming the mustache, it is a clear contravention of the Prophet's command (peace be upon him) and his established guidance, for he said: "Be different from the polytheists; let your beards grow and trim your mustaches." Thus, one who shaves his beard resembles the polytheists and contravenes the Prophet's command (peace be upon him). The Prophet was described as having a thick beard.