What is the evidence for the obligation of making up and expiating for whoever delays making up Ramadan until the next Ramadan arrives, and what is the value of this expiation?

The majority of scholars hold the view that expiation (fidyah) is obligatory for whoever delays making up (qaḍāʾ) missed days of Ramadan without a valid excuse until the next Ramadan begins. This is based on the fatwa of a group of Companions to that effect, and because delaying the make-up of Ramadan beyond its time, if it does not necessitate immediate make-up, then it necessitates expiation, similar to an elderly person. Some scholars, however, are of the opinion that expiation is not obligatory. The expiation is to feed a poor person. According to the Shafi'is, it is one mudd of food (approximately 750 grams). According to the Hanbalis, it is one mudd of wheat, or half a ṣāʿ of other types of food (approximately 1.5 kilograms), which is the more cautious approach.