Sayyiduna al-Bara' bin Azib (may Allah be pleased with him) says: On the day of Eid al-Adha the Messenger of Allah (peace and blessings be upon him) came towards al-Baqi'. He (peace and blessings be upon him) prayed two rak'ahs there, then turned towards us and said: "Our first act on this day of ours is to begin with the prayer, then to offer our sacrifice. Whoever does that has attained our Sunnah, and whoever slaughters before that, it is only meat which he has hastened for his family; it is not a sacrifice." My maternal uncle stood up and said: "O Messenger of Allah! I have already slaughtered, and I have a jadha'ah which is better than a musinnah?" He (peace and blessings be upon him) said: "Slaughter it, but after you a jadha'ah will not suffice for anyone."
Zubayd (may Allah have mercy on him) says: I heard some of our companions say: "A jadha'ah of a goat."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب صلاة العيدين / 6263