Is it permissible to command people to do or refrain from something, citing faith in Allah and the Last Day?

It is permissible to say, "Whoever believes in Allah and the Last Day, let him do such and such," if the command or prohibition is related to traits of faith, such as honoring one's parents or not disobeying them. Many hadiths in the Sunnah have used this style to encourage good and warn against evil, such as the Prophet's (peace be upon him) saying: "Whoever believes in Allah and the Last Day, let him not harm his neighbor."