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."
أخبرنا أبو داود سليمان بن سيف قال حدثنا الحسن وهو ابن أعين وأبو جعفر يعني النفيلي قالا حدثنا زهير قال حدثنا أبو الزبير
قال رسول الله ﷺ لا تذبحوا إلا مسنة إلا أن يعسر عليكم فتذبحوا جذعة من الضأن
Related by Muslim in the Book of Udhiya, Chapter on the Age Suitable for the Udhiya, hadith no. 1963, from the hadith of Zuhayr bin Muawiya, through this route, and it is also in Kubra, hadith no. 4468.Abu Zubayr explicitly stated that he heard it directly, as recorded by Abu Awana.