What is the ruling on a worshiper racing the Imam in prayer or lagging behind him?

For the ma'mum (follower) with his imam (leader), there are four situations:

1. Preceding (As-Sabq): This is when the ma'mum precedes his imam in a pillar of prayer. This is forbidden and a major sin. The prayer of one who precedes knowingly and rememberingly is nullified, but his prayer is valid if he is ignorant or forgetful, with the obligation to return if the excuse ceases before catching up with the imam. 2. Lagging Behind (At-Takhaluf): With an excuse: The ma'mum performs what he lagged behind in and follows the imam, and there is no blame on him, even if the lagging was by a full rukn (pillar) or two rukns. If the imam reaches the position of the ma'mum, the ma'mum remains with the imam, and a combined rak'ah is valid for him. Without an excuse: This is divided into: Lagging in the rukn: That the ma'mum delays following but catches up with the imam in the rukn he transitioned to. This is valid but contrary to the Sunnah. Lagging by a rukn: That the imam precedes him by a full rukn. This nullifies the prayer, whether it is ruku' (bowing) or anything else. 3. Coinciding (Al-Muwafaqah): In utterances: This is not harmful except in the takbirat al-ihram (opening takbir) and the taslim (salutation of peace). Coinciding in the takbirat al-ihram nullifies the prayer, and in the taslim it is disliked. As for other utterances, coinciding, preceding, or delaying in them is not harmful. In actions: This is disliked, and what is prescribed is following. 4. Following (Al-Mutaba'ah): This is the Sunnah, and it means that the ma'mum begins the actions of prayer immediately after his imam begins, without coinciding. So, when the imam bows, the ma'mum bows, and when he prostrates, he prostrates after him, even if he has not completed the recommended recitation or supplication in prostration.