How sound is the hadith from Ibn Abbas: "He will decay just as all other humans decay," concerning the Messenger, peace and blessings be upon him, and does its authenticity contradict the fact that the bodies of prophets are not consumed by the earth?

This hadith is one of those that enemies of Islam have trumpeted to cast doubt upon the prophethood of the Messenger of Allah, may Allah bless him and grant him peace. Scholars have weakened this hadith or ruled it as Munkar (rejected) and weak. Even assuming its authenticity, what Al-Abbas, may Allah be pleased with him, said was not a report of an event that occurred, but rather an ijtihad (independent reasoning) based on his assumption that the body of the Messenger of Allah, may Allah bless him and grant him peace, would be subject to what afflicts other bodies after death. This does not contradict the fact that the bodies of prophets are preserved from being consumed by the earth, for his noble body does not decay or change its fragrance; rather, it is more fragrant than musk.