That is, if he bows and rises before his imam bows, then prostrates before the imam rises, his prayer is invalid, because he has preceded the imam by two pillars. However, using bowing as the example is somewhat questionable, because this issue is the third category: preceding by two pillars, which can only occur in matters other than bowing. This category has two cases:

1. That he does so knowingly and deliberately, in which case his prayer is invalid.
2. That he does so out of ignorance or forgetfulness, in which case only his rak‘ah is invalid—unless he performs this after his imam.

The categories of preceding the imam may be summarized as follows:

1. Preceding the imam in reaching a pillar.
2. Preceding the imam by the pillar of bowing.
3. Preceding the imam by a pillar other than bowing.
4. Preceding the imam by two pillars other than bowing.

In summary, a follower’s preceding his imam is prohibited in all its categories. As for whether it invalidates the prayer, the rulings fall into the following categories:

First: preceding the imam in the opening takbir—for example, saying the opening takbir before the imam or along with him. In that case, the follower’s prayer does not commence, and he must say the takbir after his imam’s takbir. If he does not do so, he must repeat the prayer.

Second: preceding the imam in reaching a pillar—for example, bowing before his imam or prostrating before him. He must return and perform it after his imam. If he does not do so knowingly and deliberately, his prayer is invalid; but if he is ignorant or forgetful, his prayer is valid.