[Machine] Abdullah bin Umar used to say, "Whatever is less than a camel or a cow cannot be considered as a valid sacrifice." Ali and Ibn Abbas also said the same. This is based on the statement of Ata bin Abi Rabah, Al-Hasan, Sa'id bin Jubair, Ibrahim An-Nakhai, and others.
أَنَّ عَبْدَ اللهِ بْنَ عُمَرَ كَانَ يَقُولُ مَا اسْتَيْسَرَ مِنَ الْهَدْيِ بَدَنَةٌ أَوْ بَقَرَةٌ وَبِقَولِ عَلِيٍّ وَابْنِ عَبَّاسٍ نَقُولُ؛ لِوُقُوعِ اسْمِ الْهَدْيِ عَلَى الشَّاةِ وَهُوَ قَوْلُ عَطَاءِ بْنِ أَبِي رَبَاحٍ وَالْحَسَنِ وَسَعِيدِ بْنِ جُبَيْرٍ وَإِبْرَاهِيمَ النَّخَعِيِّ وَغَيْرِهِمْ