What is the ruling on praying behind an imam who is employed by the state and receives a salary for leading congregational prayers?

It is permissible to receive sustenance from the public treasury for Imamate and similar positions, because it falls under the category of assistance (i'anah) and not wages (ujrah). This is what Al-Kharshi, Sheikh Al-Islam Ibn Taymiyyah, the Permanent Committee, and Sheikh Al-Uthaymeen have stipulated.