Musannaf Ibn Abi Shayba 26:470

Waki’ narrated to us, he said: If they were two brothers, and one of them claimed a brother [as a third brother] while the other denied him, he said: Ibn Abi Layla used to say: It is out of six; for the one who did not make the claim, three [shares]; for the claimant, two shares; and for the one claimed [as a brother], one share. He said: And Abu Hanifa said: It is out of four; for the one who did not make the claim, two shares; for the claimant, one share; and for the one claimed [as a brother], one share.