ENOfficial
Jabir reported God's Messenger as saying, "Sacrifice only a full- grown animal unless it is difficult for you, in which case sacrifice a she-lamb.” Muslim transmitted it.
Source: sunnah.com
Other translations
Arabic
وَعَنْ جَابِرٍ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «لَا تَذْبَحُوا إِلَّا مُسِنَّةً إِلَّا أَنْ يَعْسُرَ عَلَيْكُمْ فَتَذْبَحُوا جَذَعَةً مِنَ الضَّأْن» . رَوَاهُ مُسلم
sunnah.com