Although I still would like an answer to my OP as to WHY Muslims believe all prophets are sinless. They keep dancing around it.
The intellectual rationale behind this belief is summarized by Shaykh Al-Tusi in the following quote
“Infallibility is necessary for a prophet so that surety in him is attained, and as a result, the purpose of creation is fulfilled.”
in other words a prophet must be infallible so that mankind can trust the revelation he brings. Since God has sent his prophet’s to guide mankind, he must send a person who is neither careless nor forgetful, much less sinful. If not, He will contradict His own purpose in sending prophets, revelation and in essence, the purpose of creation itself.
If the prophets were capable of carelessness, forgetfullnes, or sin, people would never fully trust that what they say is from God. They would always entertain the possibility that the prophets have lied to them or made a mistake or misunderstood God’s intent.
This belief is based on another principal belief, Divine Justice (Adl).
God is free from injustice and does not wrong a soul.
If a prophet were to make a mistake in receiving or conveying revelation, this mistake would demonstrate either ignorance, weakness, or incompetence in God’s action because the prophet’s error could be the cause of people’s misguidance.
The verses of Quran that support this belief are too many to enumerate, here are a few.
“we did not send any prophet, except so that he may be obeyed by the will of Allah.” (Quran 4:64)
"(Satan said to God) Without a doubt, I shall misguide them (mankind)
except those who are chosen from amongst them (Quran 38:82)
“Remember also our servants Abraham, Isaac, and Jacob. They were resourceful, and possessed vision.
We bestowed upon them a great blessing: awareness of the Hereafter.
They were chosen, for they were among the most righteous.” (Quran 38:45-47)
“And we granted him Isaac and Jacob, and
we guided both of them. Similarly, we guided Noah before that, and from his descendants (we guided) David, Solomon, Job, Joseph, Moses, and Aaron. We thus reward the righteous.
Also, Zachariah, John, Jesus, and Elias; all were righteous.
And Ismail, Elisha, Jonah, and Lot; each of these we distinguished over all the people.
From among their ancestors, their descendants, and their siblings, we chose many, and we guided them in a straight path.” Quran 6:84-87
“And whomever GOD
guides, nothing can send him astray. Is GOD not Almighty, Avenger?” (Quran 39:37)
In summary, God wants us to Obey the prophets that he chose satan admits he has no power over the chosen
The prophet’s can not be led astray because God guided them.