Is it obligatory for whoever leads the prayer as an imam to make an intention for the prayer? And what should he say?

Intention (niyyah (definition)) is obligatory for every worshipper, and its place is the heart; it is not permissible to utter it. As for the intention of leading the prayer (imamah), it is not a condition for the validity of the congregational prayer (iqtida'), but rather it is recommended for the Imam. Some scholars are of the view that the Imam does not attain the virtue of congregational prayer if he does not intend it, while others hold that he does attain it if a group follows him in prayer and he was unaware of their presence.