Musannaf Ibn Abi Shayba 13:1725

Abu Bakr narrated to us, he said: Ibn Numayr narrated to us, from Abd al-Malik, from Ata’, that he used to see no harm in *salam* (forward sale) for animals. And that a man may take [an animal] of a different age than what was stipulated—whether younger or older—if the soul of the giver and the taker are pleased with that.