What should one do who joins the congregation praying Asr while he has not prayed Dhuhr, or Maghrib while he has not prayed Asr, or Isha while he has not prayed Maghrib, taking into consideration the Maliki school of thought?

The website answers according to the strongest evidence. Malikis believe that one of the conditions for following an Imam is the equality of the Imam's and the follower's prayers. Thus, it is not permissible for someone praying Dhuhr to follow someone praying Asr, and vice versa. However, the preponderant opinion on the website is the permissibility for the follower to pray behind the Imam even if their prayer intentions differ. Therefore, it is permissible for someone who has not prayed Dhuhr to follow an Imam praying Asr with the intention of Dhuhr, and for someone who has not prayed Asr to follow an Imam praying Maghrib with the intention of Asr. The follower then completes their prayer after the Imam's Taslim. As for praying Maghrib behind someone praying Isha, the previously issued fatwa permitted it. However, some scholars have since preferred its impermissibility due to the obligation for the follower to differ from the Imam. In this scenario, the person praying Maghrib would either have to perform Taslim before their Imam, or wait for him and perform Taslim with him without following, or pray four rak'ahs, which is impermissible.