The Messenger of Allah ﷺ as saying: Sacrifice only a full-grown animal unless it is difficult for you, in which case sacrifice a lamb. (Using translation from Abū Dāʾūd 2797)   

قَالَ رَسُولُ اللهِ ﷺ لَا تَذْبَحُوا إِلَّا مُسِنَّةً إِلَّا أَنْ يَعْسُرَ عَلَيْكُمْ فَتَذْبَحُوا جَذَعَةً مِنَ الضَّأْنِ  

[Machine] We were on a raid, and with us or against us was Mujashi'i ibn Mas'ud, the companion of the Messenger of Allah ﷺ . The sheep became scarce, so he said, "I heard the Messenger of Allah ﷺ say, 'The offspring will be done to death as much as the adult.'  

كُنَّا فِي غَزَاةٍ مَعَنَا أَوْ عَلَيْنَا مُجَاشِعُ بْنُ مَسْعُودٍ صَاحِبُ رَسُولِ اللهِ ﷺ فَعَزَّتِ الْغَنَمُ فَقَالَ سَمِعْتُ رَسُولَ اللهِ ﷺ يَقُولُ يُوَفِي الْجَذَعُ مِمَّا يُوَفِي مِنْهُ الثَّنِيُّ