What is the ruling regarding someone who did not pray Asr until the time of Maghrib entered, while being near the mosque, knowing that the time for Maghrib is short and does not accommodate praying Asr?

The preponderant view is that the time for Maghrib prayer is extended, lasting from sunset until the disappearance of the red twilight. This period is sufficient for performing both Asr and Maghrib prayers. If someone misses the Asr prayer due to an excuse, such as sleep or forgetfulness, there is no sin upon them. However, they should hasten to perform it and observe the proper sequence between the two prayers, starting with Asr and then Maghrib. If they find a congregation praying Maghrib, they may intend to pray Asr behind the Imam, then complete their prayer after the Imam finishes. This is the opinion of Imam Shafi'i and a group of scholars. However, it is more cautious to pray Asr individually and then join the congregation for whatever part of Maghrib they catch.