What is the ruling when a forward sale of a measure of grain stipulates that part of the price is paid immediately and the rest is deferred?

Primary text

If one enters into a contract to sell a measure of grain for a hundred dirhams, stipulating that fifty dirhams are paid immediately and fifty are deferred, the entire contract is invalid according to al-Kharqi's view. Two opinions exist regarding the validity of the portion paid immediately, based on the principle of splitting the transaction. One opinion, held by Abu Hanifa, states that the part paid immediately is valid. The sounder view, held by al-Shafi'i, is that the entire contract is void because the immediate payment carries an advantage over the deferred payment, which would necessitate a greater amount in exchange for the immediate payment, and any surplus is unknown, rendering it invalid.