Sahih Muslim 1961
Sahih Muslim · Book 35: The Book of Sacrifices · The time for sacrifice
وَحَدَّثَنَاهُ ابْنُ الْمُثَنَّى ، حَدَّثَنِي وَهْبُ بْنُ جَرِيرٍ ، ح وَحَدَّثَنَا إِسْحَاقُ بْنُ إِبْرَاهِيمَ ، أَخْبَرَنَا أَبُو عَامِرٍ الْعَقَدِيُّ ، حَدَّثَنَا شُعْبَةُ ، بِهَذَا الإِسْنَادِ . وَلَمْ يَذْكُرِ الشَّكَّ فِي قَوْلِهِ هِيَ خَيْرٌ مِنْ مُسِنَّةٍ .
This hadith has been narrated on the authority of Shu'ba with the same chain of transmitters, but did not mention tht doubt (expressed in his statement) That is (the goat of less than a year) is better than a goat of more than one year.