מלכים ב ה:יג פירוש: רש״י

“My father [master].” אָבִי [lit., my father, means] the same as אֲדוֹנִי [=my master].⁸We find instances where אָב is a title that is used for prominent people. See Bereishis 45:8.

Would you not do it? Wouldn’t you do it, even if he told you to do something requiring exertion?

Certainly since. By a fortiori conclusion, for he said to you [to do] an easy thing, “immerse yourself and become clean.”