EXOD955 Our Rabbis taught: Seven things did Rabbi Akiba charge his son, Rabbi Joshua: My son... Do not enter your own house suddenly, and all the more your neighbor’s house... Rashi on this passage: “Do not enter your house suddenly,” but rather call out to them [those inside] before you enter in case they are engaged in something private. Rabbi Yohanan, when he would go to visit [Rabbi Hanina] would knock at the door, as it says, “its voice should be heard when he comes into the sanctuary” (Exodus 28:35). Babylonian Talmud, Pesahim 112a (cf. Niddah 16b).