«وَهُمْ يَنْهَوْنَ عَنْهُ وَيَنْأَوْنَ عَنْهُ»
“They forbid others from it, while themselves keeping away from it.”
Yanhawna and yanʾawna are similar in sound but differ in the identity of a letter: h versus hamzah. This is substitution, not insertion of an additional letter.
The meanings also differ: one is to forbid, the other to withdraw. The close sounds allow a sharp comparison of two related behaviors.