His statement, “before the parties separate”: receipt must also take place before the parties leave the session in which the contract was concluded. Even if we rise from the place and walk away together—for example, I enter into a salam contract with him for one hundred ṣāʿs of wheat in exchange for one hundred dirhams, but I do not have the one hundred dirhams with me. So we both go to one of my friends, I borrow one hundred dirhams from him, and give them to the man—this is permissible, because we have not separated.
We have a principle: it is a condition regarding the payment and the commodity that there be no ribā al-nasīʾah (usury arising from deferment) between them. If ribā al-nasīʾah applies between them, it is not valid to make one of them the subject of a salam contract in exchange for the other. This is because, where ribā al-nasīʾah applies, immediate mutual receipt is required, whereas salam requires deferment; and these two requirements are incompatible. Thus, if you enter into a salam contract for wheat in exchange for dates, it is not permissible; and if you enter into a salam contract for gold in exchange for silver, it is not permissible.
His statement, “If he receives part of it and they then separate, it is invalid with respect to the remainder”: “part of it” means part of the payment. Thus, if, for example, he enters into a salam contract involving one thousand dirhams for one hundred ṣāʿs of wheat, but gives him only five hundred dirhams, then what is valid is the five hundred, in exchange for which he is entitled to fifty ṣāʿs; the remainder is invalid, because receipt of the entire payment is required. Whatever has not been received is invalid. This is based on the previously mentioned sound view that a composite transaction may be divided. But if we hold that it may not be divided, then the entire contract is invalid.
His statement, “If he enters into a salam contract for one type of goods with two delivery dates”: an example is that he enters into a salam contract with someone for wheat in exchange for one thousand riyals, but stipulates that part of it falls due in Rajab and the other part falls due in Shawwal. He has thus entered into a salam contract for one type of goods with two delivery dates.
His statement, “or the reverse”: that is, he enters into a salam contract for two types of goods with one delivery date, by contracting for wheat and barley to be delivered on one date.