Sayyiduna Anas bin Malik (may Allah be pleased with him) said that on the day of Khaybar, a companion stood up and said: "O Messenger of Allah! The donkeys have been eaten," or he said: "The donkeys have been finished (by eating them)." Then he said: "O Messenger of Allah! The donkeys have been finished," or "have been eaten." Thereupon, the Messenger of Allah (peace and blessings be upon him) ordered a companion to announce: "Indeed, Allah and His Messenger both forbid you from eating the meat of domesticated donkeys because they are impure."
Hadith Referenceسنن دارمي / من كتاب الاضاحي / 2030
From these hadiths, the prohibition of mut‘ah and the flesh of donkeys is established.
Nikah al-mut‘ah is that a man contracts marriage for a specified period, such as a week, ten days, a month, or a year. This was permissible at the beginning of Islam, then it was declared prohibited until the Day of Judgment. Further details will follow ahead.
Similarly, the flesh of donkeys was lawful, then its consumption was prohibited until the Day of Judgment.
Those who hold the view of permissibility regarding these two matters—their argument is not correct, and the evidence for prohibition is clear, explicit, and strong.