Sforno on Exodus 18:6/ספורנו על שמות י״ח:ו׳

1אני חותנך יתרו, Yitro sent this message as a matter of courtesy so that Moses would not be taken unawares by his sudden arrival. He complied with the sages’ warning “do not enter your own house without advance notice, how much more so the house of your friend.” (Pessachim 112).