Is it permissible for someone who enters the mosque and finds an Imam whom he does not wish to pray behind, to pray entirely alone, separate from him?

The evidence for the obligation of congregational prayer is abundant, and a Muslim must pray with the congregation at the mosque even if he dislikes the Imam, as Al-Hasan (definition) said: "Pray, and his innovation is upon him," and as 'Uthman ibn 'Affan, may Allah be pleased with him, said: "Prayer is the best of what people do. So, if people do good, then do good with them, and if they do evil, then avoid their evil." Sheikh Ibn 'Uthaymeen clarified that whoever enters the mosque to pray must pray with the congregation, even if he dislikes the Imam, because congregational prayer is obligatory, and it is not permissible for him to neglect it. If the dislike is due to a deficiency in the Imam's religiosity, then he must advise him. As for people abandoning each other, or harboring malice and animosity, that is contrary to the state of believers. However, whoever acts contrary to this and prays alone has done wrong, but his prayer is valid, for congregational prayer is not a condition for the validity of the prayer. And whoever prays alone while a congregation is present and he is able to attend, he has sinned, but his prayer is valid.