It is narrated from Nafi' (may Allah have mercy on him) that Abdullah bin Umar (may Allah be pleased with them both) used to say: By "whatever is easy from the sacrificial animal" is meant the sacrifice of a camel or a cow.
Hadith Referenceمسند الإمام الشافعي / كتاب الحج / 835
Hadith Takhrijاسناده صحيح اخرجه مالك في المؤطا ، الحج، باب ما استيسر من الهدى والبيهقي : 24/5 ۔ وفي المعرفة السنن والآثار له ۔ (374) وابن ابی شیبه (12778) ،(12781) ، (12788)۔
It is narrated from Nafi' (may Allah have mercy on him) that it is reported from Ibn Umar (may Allah be pleased with them both) that he did not consider it objectionable whether the (camel's) right side was marked or the left side.
Hadith Referenceمسند الإمام الشافعي / كتاب الحج / 837
Hadith Takhrijاسناده ضعيف لضعف مسلم بن خالد ولعنة ابن جريج : اخرجه البيهقى 232/5 - وفي المعرفة السنن والآثار له (3281)۔