What is the ruling on joining the row after completing the bowing phase (ruku) when the person was fully aware of the prohibition?
Chapter on Imamate and Congregational Prayer
Al-Mughni
Book of Prayer
Primary text
If one raises his head from ruku and then enters the row, or another joins him before completing the rak'ah, and he was aware of the prohibition, his prayer is invalid. If he was ignorant, his prayer is valid, according to one interpretation of Imam Ahmad's view cited by Al-Kharqi. However, Abu Dawud narrated from Ahmad that it is valid regardless of knowledge, and this view is supported by Malik, Al-Shafi'i, and the People of Opinion, based on the incident of Abu Bakra where the Prophet (PBUH) did not order him to repeat the prayer but forbade him from repeating the action.
Supporting text
Another narration from Imam Ahmad states the prayer is invalid whether the person knew or was ignorant, because he did not attain the part of the rak'ah while in the row, similar to someone missing the entire rak'ah. Al-Qadi did not differentiate between bowing before or after rising from ruku, although the evidence suggests differentiation should be made, and Abu Al-Khattab mentioned this differentiation.