Musannaf Ibn Abi Shayba 13:3355

Abu Bakr narrated to us, he said: Hushaym narrated to us, from Mughira, from Ibrahim, regarding a man who bought a sale for such-and-such [price] for one month, and for such-and-such [price] for two months, and he kept that sale secret. He said to him: [It shall be] the lesser of the two prices for the longer of the two terms.