It is best to wait for the Imam to complete his Takbir before commencing.
قَالَ: «إِنَّمَا جُعِلَ الإِمَامُ لِيُؤْتَمَّ بِهِ، فَإِذَا رَكَعَ فَارْكَعُوا، وَإِذَا رَفَعَ فَارْفَعُوا»
The Prophet ﷺ said, ‘The Imam is to be followed. So if he bows then bow, and if he rises then rise (from bowing).’ (Sahih al-Bukhari, 1113).
There is no doubt that one must follow the Imam and not precede him in Salah, doing so is certainly Makruh and can sometimes invalidate the Salah.
وَيُكْرَهُ لِلْمَأْمُومِ أَنْ يَسْبِقَ الْإِمَامَ بِالرُّكُوعِ وَالسُّجُودِ وَأَنْ يَرْفَعَ رَأْسَهُ فِيهِمَا (الفتاوى الهندية)
And it is Makruh (disliked) for the follower to perform Ruku, Sujood or rise from them before the Imam. (al-Fatawaa al-Hindiyah).
So, as long as a person does not precede the Imam then he has avoided Karahah (dislike). But what is meant by following the Imam? This is sometimes differed over, and therefore the most preferable approach is differed over.
وَالْأَفْضَلُ أَنْ يُكَبِّرَ الْمَأْمُومُ مُقَارِنًا لِتَكْبِيرِ الْإِمَامِ وَعِنْدَهُمَا بَعْدَهُ، وَفِي السَّلَامِ بَعْدَهُ بِالِاتِّفَاقِ (الاختيار لتعليل المختار)
And it is best for the follower to make Takbir at the same time as the Imam (according to Imam Abu Hanifah). According to them both (the Saahibayn) the follower is to make Takbir after the Imam. As for Salam, it is to be made after the Imam by agreement. (Imam al-Mowsili, al-Ikhtiyaar).
In the above text we see that Imam Abu Hanifah sometimes considered performing actions at the same time as the Imam to be the correct position and sometimes after the Imam. However, the Saahibayn preferred one to wait for the Imam to finish. This position is best to follow since it is more cautious and keeps the follower further away from Karahah (dislike).
And Allah (Most High) Knows Best.
– Answered by Shaykh Noorud-deen (22.04.2021)
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