Abu al-Khasib, a man of Banu Qays bin Tha'labah, came to Sayyiduna Abdullah bin Umar (may Allah be pleased with them both), and a man asked him about something concerning the sacrifice. He said: I dislike, or (he said) avoid (Wahb was in doubt): "the one-eyed animal whose loss of the eye is evident, the lame animal whose lameness is evident, the sick animal whose sickness is evident, and the emaciated animal whose emaciation is evident." Then Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) said: Perhaps you consider it binding? He said: No, but it is reward, good and sunnah. He said: Yes, that is so.
Imam al-Shafi'i (may Allah have mercy on him) said: The view on sacrifices does not go beyond this, or else they are obligatory, in which case they would be upon everyone, young and old, and nothing less than a sheep would suffice for each person.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / 19040