من نسي فرضا من فرائض الصلاة

All praise is due to Allah, and peace and blessings be upon the Messenger of Allah, his family, and his companions. To proceed: If a pillar of prayer is omitted and cannot be rectified, then the rak'ah (unit of prayer) containing that pillar is invalid. The worshipper must then perform another rak'ah in its place, followed by the prostration of forgetfulness (sujud as-sahw). The basis for this is what was narrated by the group of scholars in the hadith of Abu Hurairah (may Allah be pleased with him), and the wording is from Muslim: He said: The Messenger of Allah (peace and blessings be upon him) led us in one of the afternoon prayers, either Dhuhr or Asr. He concluded after two rak'ahs. Then Dhu al-Yadayn stood up and said: O Messenger of Allah, has the prayer been shortened, or did you forget? The Prophet (peace and blessings be upon him) looked to his right and left and said: What is Dhu al-Yadayn saying? They said: He is right. You only prayed two rak'ahs. So he prayed two more rak'ahs and concluded, then he said the takbir (Allahu Akbar), then he prostrated, then he said the takbir and rose, then he said the takbir and prostrated, then he said the takbir and rose. If he does not do this until a long time has passed or his ablution is invalidated, then the prayer is invalid, and he must repeat it. The length of the interval is determined by custom. Some scholars have said that one may continue from where one left off in prayer and complete the remainder, even if the interval is long, as long as one's ablution remains valid. However, the first opinion is the more reliable. In al-Mughni, it states: "If the interval is long or one's ablution is invalidated, one must start the prayer anew... Yahya al-Ansari, al-Layth, and al-Awza'i said: one may continue as long as one's ablution remains valid... and the length of the interval is determined by custom without any fixed measure." (1/374). Therefore, these followers must repeat their prayers because they are invalid if they omitted a pillar such as bowing. And Allah knows best. Related Materials Fatwas Audio Library Ruling on someone whose doubts during prayer are so frequent as to resemble obsessive-compulsive disorder The follower's failure to follow the imam in the prostration of forgetfulness and in exiting the prayer with a single salutation Rulings on the prostration of forgetfulness for one who joins the prayer late Interrupting and repeating the prayer due to ignorance of the rulings on the prostration of forgetfulness The obligation of one who recites the opening supplication after seeking refuge with Allah The imam is not responsible for the latecomer's forgetfulness after the final salutation One who forgets the prostration of forgetfulness, which is performed before the final salutation, and remembers it after the final salutation