Sayyiduna Jabir (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) said: "Sacrifice a two-toothed animal. If it becomes difficult for you, then slaughter a jadha'ah of sheep."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 10164
Asim bin Kulayb narrated from his father: With us on a military expedition was Mujashi' bin Mas'ud (may Allah be pleased with him), a Companion of the Prophet (peace and blessings be upon him). Sheep became scarce, so he said: I heard the Messenger of Allah (peace and blessings be upon him) saying: "A jadha' suffices just as a two-toothed animal (thani) suffices."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 10165