Is it to be understood from what Ibn ‘Umar and Abu Hurayrah did, and the fact that the people said takbeer when they heard their takbeer, that this was takbeer in unison?
Question

                We hear that saying takbeer in unison is bid‘ah and is not permissible; what do these scholars say about that? Is it possible to quote as evidence for the permissibility of saying takbeer in unison the report which says that Ibn ‘Umar and Abu Hurayrah (may Allah be pleased with them) used to go out in the marketplace and say takbeer, and the people would say takbeer when they heard their takbeer?

If we say that the people used to say takbeer individually, each one saying his own takbeer, then how did the people say takbeer when Abu Hurayrah and Ibn ‘Umar said takbeer, if they were not saying takbeer together? If we say that they were walking in the marketplace and saying takbeer, did the people divide into two groups, one group on the right, for example, saying takbeer with Abu Hurayrah and the group on the left saying takbeer with Ibn ‘Umar? If it is said that they walked separately in the marketplace, each one saying takbeer in a different place, the hadith does not indicate that; if that was the case, it would have been mentioned in the hadith.
Praise be to Allah.
      We have previously discussed the ruling on saying takbeer 
      in unison, and we have quoted the opinions of the scholars concerning 
      that. We have also stated that quoting the report narrated by al-Bukhaari 
      in his Saheeh (2/20) – which says that Ibn ‘Umar and Abu Hurayrah 
      used to go out to the marketplace on the first ten days of Dhu’l-Hijjah 
      saying takbeer, and the people would say takbeer with their takbeer – to 
      suggest that it is prescribed to say takbeer in the manner that is done 
      nowadays, reciting takbeer in unison, is a view that is subject to doubt 
      and further discussion. 

    Please see fatwa 127851. 

    To sum up: Abu Hurayrah (may Allah be pleased with him) and 
    Ibn ‘Umar (may Allah be pleased with him) used to go out to the marketplace 
    and say takbeer in that place where people are usually heedless because they 
    are distracted, so people will be reminded by the takbeer, and each one will 
    say takbeer on his own, after that reminder, so the numbers of those who say 
    takbeer will be many as a result of that. 

    This has nothing to do with dividing people into two groups, 
    or whatever else was mentioned of such made-up things for which there is no 
    basis in the reports at all. 

    With regard to the words of ash-Shaafa‘i in al-Umm 
    (1/264): When they see the new moon of Shawwaal, I like for the people to 
    say takbeer in groups and individually, in the mosque, marketplaces, streets 
    and homes, both travellers and non-travellers, in all situations, wherever 
    they are, and for them to say the takbeer out loud, and to continue to say 
    takbeer until they go out to the prayer-place [on the day of Eid al-Adha], 
    and after sunrise, until the imam comes out for the prayer, then they should 
    stop saying takbeer. End quote – 

    this is not speaking of takbeer in unison as it is known 
    nowadays, in which they all start together and end together, and we have not 
    come across anything to that effect in the books of his companions, even 
    though they paid a great deal of attention to details in such matters, to 
    the extent that they devoted chapters to the “takbeer” or the “takbeer on 
    the two Eids” in many of their books. 

    What appears to be the case, and Allah knows best, is that it 
    is to be understood as meaning that each one should say takbeer, whether he 
    is on his own or with a group, all of whom are saying takbeer, in the mosque 
    or any other place that he mentioned, without them all doing so in unison. 

    It is well-known that if the text is ambiguous, in that case 
    it cannot be used as evidence, therefore what we mentioned in the fatwa 
    referred to above is not contradicted by any text. 

    However we should point out that the view that this kind of 
    saying takbeer in unison is an innovation is not a recent view; rather it 
    was stated by leading scholars a long time ago, including Ibn al-Haaj, who 
    said in his book al-Madhkal (2/285), when discussing the takbeer of Eid: 
    Moreover they recite takbeer in unison,and that is an innovation, because 
    what is prescribed is for each person to say takbeer for himself, and not to 
    say it in unison with others. End quote. 

    And Allah knows best.