It is related that Ibrahim an-Nazzam had come together with Manasse bin Salih the Jew and Manasse said to Ibrahim; "If God has ordained a divine Law is it not true that he would only order pure wisdom?"
Then Manasse said: "It is impossible for you then, that God has ordained a divine Law, and it was enacted for some time, then He ordered its complete invalidation and a different way of action. So if He prohibited doing what He ordered, He is forbidding enactment of wisdom".
Ibrahim replied: "Indeed there are two types of wisdom: the pure wisdom, having no reason for it, like justice, faith truthfullness and acts of kindness. These things are never abrogated by God. And there is wisdom which becomes wisdom because of aim for which it is ordered, like worship, prayer, fasting; whatever of this God has ordained is good and of superior wisdom, and were He to abrogate that and command something else, it would be wise to obey that too. However, the wisdom in it is the preference of obedience to God and of submission to His will, because its results are good. He ordains it, and obedience to it is wisdom, then He forbids it and orders something else, but obedience to Him in it too - this is wisdom. But this is not the same with the truth which is good forever and opposite to it is bad.
Manasse said: "Can it be denied that the Law of Moses which was ordained is exellent and therefore its abrogation is impossible?
Ibrahim answered: "It is not impossible. For if it is good by reason of its substance people know it is good, whether it is brought by a Prophet or not. The latter is like doing good deeds to a good person, or abstaining from injustice and observing truth. As for Law which inform specific aims, such as prayer and fast, had they not been related by a Prophet, we would not have known that prayer is obligatory or that cessation of fasting at the time of fast is prohibited. And if Moses had not declared that work is forbidden on Shabat, we would not know that it is forbidden, and ther would be no distinction between Saturday and Sunday. And since we would not have known that these [precepts] were obligatory inbalance, except from the oral tradition, and had not the Prophet taught people to serve God thruogh this observance - we would not have known them, so it invalidates your statement that the Law of Moses is good by reason of its very substance.
Manasse said: "So is it possible that God after having enjoined people to serve Him through fulfillment of the Law revealed by the tongue of Moses and said: "This Law is upon you forever, and who does not act according to it - put him to death" and that He should abrogate it?
Ibrahim answered: "Yes. That is possible, because Moses enforced its acceptance with signs and the miraculous plagues, made people fllow the Laws and informed them that God made it obligatory and enjoined upon them. And whoever comes forward with something similar to the miraculous plagues and signs performed by Moses, then acceptance of his words is obligatoryas the acceptance of the words of Moses is obligatory. If it is possible that Jesus had been false in spite of all the miracles whichhe performed, then it is possible that all about Moses was false. Since falsehood must be negated about them, it is then established that they were truthful. The words of Moses: "This is upon you forever" are known metaforically to mean eternity, but indeed he meant by the word "forever" a long age, a fixed period. Now whoever comes after Moses does not come with suspension of any precept which God had made excellent by reason of its very substance, but he brings the abrogation of that whose positive or negative observance was enacted for a specific reason. Jeremiah the Prophet said in his book(13:13-23): "The Lord said: "I shall give Law to Israel and the house of Judah, the new observance, not like the observance I decreed for them when I brought them out of Egypt". Indeed it informs that it is possible that God orders a Law and thaen orders a different one after that.
Then said Ibrahim to Manasse the Jew: " You agree that God ordered Abraham to sacrifice his son. Is it wisdom or ignorance?"
Manasse answered: "Nothing but wisdom."
Ibrahim said: "Did not Abraham take a knife, a string, a firewood and go up to the mountain with his son to sacrifice him? And when he placed a knife on his throat, God forbade him that?"
Manasse said: "Yes."
Ibrahim said: "So did God forbid wisdom in any way?"
Manasse said: "God ordered Abraham to sacrifice his son in order to test whether he would obey him or not. Then he tested his obedience by stopping him".
Ibrahim said: "You are right. Then there is no difference between us in this. However the difference is that we say that an order for something, if He orders it, is wisdom, and prohibition from it, if He prohibited it, is wisdom too, because for us both are the order of goodness, and you dispute that."