Is it permissible to speak during an obligatory prayer, such as responding to Allah's saying: "Is not Allah the most just of judges?" with "Yes, and to that we bear witness"?

Answering verses that contain questions is recommended for the worshipper, according to some scholars like the Shafi'is, whether in obligatory or supererogatory prayers. The Hanbalis say it is not recommended in obligatory prayers, and it is disliked by the Malikis and Hanafis. Al-Kasani holds that it is disliked for the Imam to do so in obligatory prayers because the Prophet, peace and blessings be upon him, did not do it, and because it burdens the congregation. However, his prayer is not invalidated because it increases his humility. There is no difference in speech between obligatory and supererogatory prayers, as the default is that they are equal in rulings unless specified otherwise by evidence.