Chazal in a few places (Pesachim 56a and Bereishis Rabbah 98:3 for example) say that Yaakov asked his twelve sons if any of them had turned rotten, or had a lapse in faith. They responded שמע ישראל השם אלקינו השם אחד, Hear O Israel, Hashem is our G-d, Hashem is One!
Rashi in Pesachim clarifies they were referring to their father when they said Israel.
According to Kiddushin 32b, ruled by Rambam in Hilchos Mamrim 6:3, it is forbidden to refer to one's father by name. How were they able to do so in this instance? (I'm assuming they kept halacha).
Maybe one could argue there was no problem calling Yaakov by Israel, but I'd like an explanation or proof/source why.