Hussein is still a Muslim.He's a murderer. That makes him an infidel. In order to be a Muslim one must live in keeping with God's commandments. Gassing Kurdish non-combatants is enough reason to declare that he is not in keeping with those..
He is a Muslim in that he went to Mosque quite often in his life and donated some money to Muslim charity. Mafia Don is still a Catholic, too.
Is that a common teaching in Islam?
That is absolutely ridiculous.
First of all, Abraham was pre-law, meaning he had no law or commandments to obey. Hebrews 11 tells us that he was justified before God by his faith, not by any law.
Moses had a set of commandments, but they aren't used verbatim by the Muslims. One major point is that that the Jews were told to remember the Sabbath and keep it holy. The Jews uses Saturday as their Sabbath. Tell us what day the Muslims use, and do they call it the Shabbat?
That puts him in the same boat as Bin Laden and his merry band.