What is the correct intention for fasting according to the Qur'an and Sunnah, and is saying: "O Allah, I fast diligently for You, so forgive me what I have sent forth and what I have delayed" considered a correct intention?

The fast of Ramadan is not valid except with the intention (niyyah), based on the statement of the Prophet, peace and blessings be upon him: "Actions are but by intentions." It is a condition that the intention be made during the night and before Fajr, based on the statement of the Prophet, peace and blessings be upon him: "Whoever does not resolve to fast before Fajr, there is no fast for him." The intention is an act of the heart, by which a Muslim resolves in his heart that he will fast tomorrow, and verbalizing it is not prescribed. So, whoever has the thought in his heart that he will fast tomorrow has made the intention.