Musannaf Ibn Abi Shayba 3:3437

Abu Bakr narrated to us, he said: Ibn Idris narrated to us, from Layth, from al-Hakam, from Hanash, who said: It was said to Ali ibn Abi Talib that the weak among the weak people are unable to go out to the *jabbana* (the open prayer ground). So he ordered a man to lead the people in prayer with four *rak'ahs*: two *rak'ahs* for the Eid, and two *rak'ahs* for the place of their going out to the *jabbana*.