What is the ruling on one who prays Fajr and then slanders people and delves into their honor without proof?

This person is mistaken and committing grave sins. He must repent to Allah, for his persistence in these sins exposes him to a great danger: that he will be among those who are bankrupt on the Day of Resurrection, whose good deeds will go to waste because of their transgression against the rights of others. And whoever sees him should remind him of Allah and forbid him from evil.