From Fatawa Ridawiyyah, vol.7, p.234-235
Question: If the congregation is in ruku’ [bowing], then does the masbooq [latecomer] make the intention, say takbir al-tahrima and then tie the hands or does he say the second takbir and go into ruku’ without tying the hands? Or is saying only one takbir enough for him? Bayyinu Tujiru.
Answer: There is no specific need to tie the hands and saying only the takbir al-tahrima will suffice for the salah to be valid. However, the sunnah of the takbir of going into ruku’ will be lost. Hence, he should say the takbir al-tahrima in a standing position and if there is no time to read Subhaanak Allahumma [thana], i.e. he thinks that the Imam will raise his head; then he should go into ruku’ as he is saying the second takbir [of ruku’]. If he knows that the Imam takes a long time in ruku’ and the latecomer knows he has time to read Subhaanak Allahumma, then he should read it and then go into ruku’ whilst saying the [second] takbir. This is the sunnah way.
To say the takbir al-tahrima whilst standing is fard. Some ignorant people who see the Imam in ruku’ and they themselves go into ruku’ whilst saying the takbir al-tahrima - if they bowed so much that if they spread their arms they would reach the knees and they have not yet finished saying Allahu Akbar - then the salah will be invalid. It is important to take care in this matter. Wallahu ta’ala a’lam.
Question: If the congregation is in ruku’ [bowing], then does the masbooq [latecomer] make the intention, say takbir al-tahrima and then tie the hands or does he say the second takbir and go into ruku’ without tying the hands? Or is saying only one takbir enough for him? Bayyinu Tujiru.
Answer: There is no specific need to tie the hands and saying only the takbir al-tahrima will suffice for the salah to be valid. However, the sunnah of the takbir of going into ruku’ will be lost. Hence, he should say the takbir al-tahrima in a standing position and if there is no time to read Subhaanak Allahumma [thana], i.e. he thinks that the Imam will raise his head; then he should go into ruku’ as he is saying the second takbir [of ruku’]. If he knows that the Imam takes a long time in ruku’ and the latecomer knows he has time to read Subhaanak Allahumma, then he should read it and then go into ruku’ whilst saying the [second] takbir. This is the sunnah way.
To say the takbir al-tahrima whilst standing is fard. Some ignorant people who see the Imam in ruku’ and they themselves go into ruku’ whilst saying the takbir al-tahrima - if they bowed so much that if they spread their arms they would reach the knees and they have not yet finished saying Allahu Akbar - then the salah will be invalid. It is important to take care in this matter. Wallahu ta’ala a’lam.