Must I send a message containing the supplication "There is no god but You; glory be to You! Indeed, I have been of the wrongdoers," along with the pledge that it is a "trust upon one's conscience until the Day of Judgment," so that I do not become sinful?

The supplication of the Prophet Yunus (peace be upon him) in the belly of the whale is: "There is no deity except You; exalted are You. Indeed, I have been of the wrongdoers." It has been authentically reported in a hadith that whoever supplicates with it, Allah will answer him. As for the phrase "You will hear good news tonight," there is no evidence for it, and it might be one of the baseless superstitions. One should be cautious of spreading such matters or lying about the Prophet (peace and blessings of Allah be upon him), as it is forbidden by Islamic law.