The Messenger of Allah ﷺ said, "Do not sacrifice anything but a mature animal, unless that proves difficult for you, in which case you may sacrifice a young sheep."
حدثنا هارون بن حيان حدثنا عبد الرحمن بن عبد الله أنبأنا زهير عن أبي الزبير
قال رسول الله ﷺ لا تذبحوا إلا مسنة إلا أن يعسر عليكم فتذبحوا جذعة من الضأن
[Sahih] Narrated by Muslim, in the Book of Udhiya, Chapter on the Age of the Udhiya, hadith no. 1963, from the hadith of Zuhayr, through this route.Abu Zubayr explicitly stated that he heard it directly, according to Abu Awana, 5/228, and whoever judged the hadith to be daif was not correct.