Is the rak'ah counted for whoever catches the Imam during ruku' in congregational prayer, or must he repeat it?

The majority of scholars, including the four Imams, hold the view that whoever catches the Imam bowing and bows before the Imam rises has caught the rak'ah. They base this on the hadith: "Whoever catches one rak'ah of the prayer has caught the prayer," and on the action of Abu Bakrah. The Hanbalis differed in the case of catching a rak'ah alone behind the row. As for the Ahl adh-Dhahir, they believe that the rak'ah is not caught by catching the bowing, basing this on the hadith: "There is no prayer for whoever does not recite the Opening of the Book (Fatihat al-Kitab)." The correct view is that of the majority. The worshipper attains the virtue of congregational prayer commensurate with the portion of the prayer they catch, and Islamic law encourages diligence in catching the takbirat al-ihram (opening takbir).