When was fasting prescribed for nations before Islam, in the time of which Messenger, and what is the evidence for that?

There is no benefit in knowing the exact time fasting was enjoined upon previous nations, and therefore Allah did not inform us of it. Some exegetes have suggested that the intended meaning refers to Jews and Christians, but this is an unsubstantiated claim, as Allah informed us that fasting was enjoined upon those before us without specifying. A Muslim may ponder that the purpose of this information is twofold: First, to highlight and emphasize this act of worship, given that it was legislated in the divine laws of previous prophets, which implies its merit and abundant reward. Second, to make it easier for those obligated to perform it, as following the example of others serves as a solace in hardships.