Did the Messenger of Allah (peace and blessings be upon him) always begin his gatherings with: "Indeed, all praise is due to Allah; we praise Him and seek His help," or did he use other supplications? And what is the ruling on commencing gatherings with other supplications that include praising Allah and extolling Him?

The Prophet, peace and blessings be upon him, did not adhere to a specific supplication for commencing his gatherings. Therefore, a Muslim may commence their gathering with any opening supplication or prayer proven from the Prophet, peace and blessings be upon him, or by saying "Alhamdulillah" (Praise be to Allah), or "Bismillahir Rahmanir Rahim" (In the name of Allah, the Most Gracious, the Most Merciful), or simply "Bismillah" (In the name of Allah); based on his saying, peace and blessings be upon him: "Every matter of importance that does not begin with 'Bismillah' is cut off (deficient)," and in another narration: "that does not begin with 'Alhamdulillah' is cut off (deficient)."