Source: Fatawa of Ahl-e-Hadith Scholars, Kitab al-Salah, Volume 1
"When you come to the prayer and the Imam is in Ruku‘, then bow with him; and if he is in prostration, join him there, but do not count that prostration without Ruku‘." (Bayhaqi)
In Sahih Bukhari, it is reported from Abu Qatadah and Abu Hurairah (رضي الله عنهما) that the Prophet ﷺ said:
"Whatever you catch with the Imam, pray it; and complete what you missed after the Imam finishes." (Sahih Bukhari, Kitab al-Adhan)
This Hadith indicates that if someone finds the Imam in Ruku‘, the Rak‘ah will not be counted, because Qiyam and recitation have been missed.
Hafiz Ibn Hajar رحمه الله states that this Hadith proves the Rak‘ah is not counted for one who joins the Imam in Ruku‘, because it mandates completing what was missed. Since Qiyam and Qira'ah are missed in this case, the Rak‘ah cannot be considered complete.
"Whoever catches the Ruku‘ has caught the Rak‘ah."
However, these narrations are weak, and due to the unreliability of their narrators, they cannot be trusted. Shaykh Albani رحمه الله has also mentioned that most of these narrations are Mawquf or weak, and have been criticized by Hadith scholars for their chains of transmission.
Reference: Fatawa of Ahl-e-Hadith, Kitab al-Salah, Volume 1
❖ Question:
If a person finds the Imam in the position of Ruku‘ (bowing) and joins him there, will that Rak‘ah be counted for him? Some people argue by citing a narration of the Prophet ﷺ:"When you come to the prayer and the Imam is in Ruku‘, then bow with him; and if he is in prostration, join him there, but do not count that prostration without Ruku‘." (Bayhaqi)
❖ Answer:
Authentic Hadiths do not support the idea that a Rak‘ah is counted simply by joining the Imam in Ruku‘. The narrations that seem to support this view are weak, and the Hadith you referenced from Bayhaqi is also considered weak.In Sahih Bukhari, it is reported from Abu Qatadah and Abu Hurairah (رضي الله عنهما) that the Prophet ﷺ said:
"Whatever you catch with the Imam, pray it; and complete what you missed after the Imam finishes." (Sahih Bukhari, Kitab al-Adhan)
This Hadith indicates that if someone finds the Imam in Ruku‘, the Rak‘ah will not be counted, because Qiyam and recitation have been missed.
Hafiz Ibn Hajar رحمه الله states that this Hadith proves the Rak‘ah is not counted for one who joins the Imam in Ruku‘, because it mandates completing what was missed. Since Qiyam and Qira'ah are missed in this case, the Rak‘ah cannot be considered complete.
❖ The Issue of "Madrik Ruku‘" and "Madrik Rak‘ah":
Some narrations suggest:"Whoever catches the Ruku‘ has caught the Rak‘ah."
However, these narrations are weak, and due to the unreliability of their narrators, they cannot be trusted. Shaykh Albani رحمه الله has also mentioned that most of these narrations are Mawquf or weak, and have been criticized by Hadith scholars for their chains of transmission.
❖ Conclusion:
Based on authentic narrations, joining the Imam in Ruku‘ does not count as a complete Rak‘ah, since Qiyam and Qira'ah are essential and are omitted in such a case. Reference: Fatawa of Ahl-e-Hadith, Kitab al-Salah, Volume 1