(2) باب سِنِّ الأُضْحِيَةِ
Jabir reported Allah's Messenger (ﷺ) as saying:
Sacrifice only a grown-up animal, unless it is difficult for you, in which case sacrifice a ram (of even less than a year, but more than six months' age).
Reference: Sahih Muslim 1963
In-book reference: Book 35, Hadith 19
USC-MSA web (English) reference(deprecated numbering scheme): Book 22, Hadith 4836