All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
The Muslims went out to the street in Makkah forming two rows, one row was led by Hamzah and the other row was led by 'Umar and this is a well known incident which the historians mentioned. This incident was an act to show the strength of the Muslims, and it is evidence for the permissibility of organizing peaceful demonstrations that as a means of expressing oneself.
Since these demonstrations are means, then they do not need a special evidence proving their permissibility, because, in principle, means are permissible. The one who claims that such demonstrations are forbidden is required to provide evidence about their prohibition.
For more benefit, please refer to Fatwa 84082.
Allaah Knows best.