Are the Prophets innocent / infallible?
According to the traditional understanding the prophets are innocent / infallible (ismah). The Quran tells us about sins from the Nabis (Prophets) who were sent instead of angels (Fussilet  6; Kehf  110). The Nabis are humans like us. A person with an innocent / infallible attribute couldn’t be an example for us.
• “…Adam disobeyed his Lord, and fell.” (Ta-ha 20:121).
• “(Abraham:) He who, I hope, will forgive my sins on the Day of Reckoning.” (ash-Shuara 26:82).
• “When he (Jonah) fled to the laden boat.” (as-Saffat 37:140).
• “…ask forgiveness for your sins لِذَنْبِكَ and for the believing men and believing women…” (Muhammad 47:19).
• “May Allah pardon you!…” (at-Tawbah 9:43).
Therefore according to the Quran the Nabi / Rasouls (Prophets / Messengers) are not innocent / infallible. If the Nabi / Rasouls are not innocent / infallible, than masters, imams, sheikhs, scholars etc. of course could commit sins. Give nobody a half god position!
Notice: Zalla الزلّة couldn’t mean minor sin. Look to: al-Anfal 8:68.