Is it permissible for the Imam to pray in the mosque after instructing the worshippers to pray in their homes?

There is no harm for the Imam or others in praying at the mosque after the muezzin says, "Pray in your homes." The wisdom behind this is to lighten the burden for those who find it difficult to attend the mosque due to an excuse, such as rain. As for whoever is inside the mosque or has endured the hardship of attending, let them pray therein.