Is it permissible to make a collective supplication—whereby the Imam supplicates and the congregants say "Ameen"—after the five daily prayers and the Friday prayer? And does the ruling on this differ among the different schools of thought, and what is the view of the Maliki school on this?

It is permissible to supplicate after the obligatory prayer. As for congregational supplication after prayer, it is permissible as long as it is not taken as a regular habit. Ahmad prohibited its continuous practice, while some followers of Abu Hanifa and Malik permitted it, though Malik himself disliked it. Some later Maliki scholars and others permitted congregational supplication, affirming its legitimacy and stating that the practice of its permissibility continued in Africa. Al-Shafi'i deemed it desirable for the imam to depart immediately after the salutations. Al-Qarafi considered Malik's and the group's dislike of audible supplication after the prescribed prayers, while Ibn Naji held that the practice of its permissibility continued.