What is the ruling on a man imagining another woman during sexual intercourse with his wife and deriving pleasure from that?

The scholars, may Allah have mercy on them, have explicitly stated the prohibition of what this man does, namely, engaging in intercourse with his wife while imagining another woman (who is a stranger to him), because it resembles forbidden imagery and involves finding pleasure in it.

Ibn al-Hajj al-Maliki said: "This is a type of zina (fornication/adultery), and he likened it to someone who imagines wine when drinking water, thus making the water forbidden for him." The same ruling applies to the woman as well.

Ibn Muflih al-Hanbali and Ibn Aqil said: "Whoever brings to mind a forbidden image of a strange woman during intercourse with his wife commits a sin."

Wali al-Din al-Iraqi said: "It is forbidden for him to do that, due to his resemblance to forbidden imagery."