Was it narrated in authentic hadiths what the Prophet (peace and blessings be upon him) used to say when he praised Allah as He deserves before his sermon, and can this praise be used in the opening supplication (Du'a al-Istiftah) or before other supplications?

Firstly: The Prophet, peace and blessings be upon him, used to begin his sermons with praise and glorification of Allah. This has been established in many hadiths, including the hadith of Abu Hurayrah: "Every sermon that does not contain the tashahhud is like a leprous hand." The tashahhud means praising Allah and bearing witness to His Oneness and to the prophethood of Muhammad, peace and blessings be upon him. He often began with the "Khutbat al-Hajah" (Sermon of Need), which is recommended to be recited before concluding a marriage contract and in reconciliation gatherings.

Secondly: The Istiftah (opening) supplication in prayer has many forms reported from the Prophet, peace and blessings be upon him, and a Muslim should not begin with anything other than what has been reported from him, based on his saying, peace and blessings be upon him: "Pray as you have seen me praying."

Thirdly: It is sunnah to begin supplications with praise of Allah Almighty, then with blessings upon the Messenger of Allah, peace and blessings be upon him. The praise can be in any words that describe Allah Almighty with perfection. The Prophet's supplications contained much praise of Allah by mentioning His names and attributes.