A person should not enter his friend's house suddenly
It is forbidden for a person to enter another person's house unexpectedly.
("A person should not enter his friend's house suddenly. Let everyone learn proper conduct from the place where God stood at the entrance of the garden and called to Adam, as it is said: 'And the Lord God called to the man and said to him, Where are you?'" - Yalkut Shimoni, Torah, Parashat Bereshit, 27)
Translation
Expression (Hebrew)
אַל יִכָּנֵס אָדָם פִּתְאוֹם לְבֵית חֲבֵרוֹ
Definition (Hebrew)
אָסוּר לְאָדָם לְהִכָּנֵס בְּאֹפֶן מַפְתִּיעַ לְבֵית אָדָם אַחֵר.
("אַל יִכָּנֵס אָדָם פִּתְאוֹם לְבֵית חֲבֵרוֹ. וְיִלְמְדוּ כָּל אָדָם דֶּרֶךְ אֶרֶץ מִן הַמָּקוֹם שֶׁעָמַד עַל פֶּתַח הַגַּן וְקָרָא לוֹ לְאָדָם,שֶׁנֶּאֱמַר: וַיִּקְרָא ה' אֱלֹהִים אַל הָאָדָם וַיֹּאמֶר לוֹ אֵיכָה"- יַלְקוּט שִׁמְעוֹנִי תּוֹרָה פָּרָשַׁת בְּרֵאשִׁית רֶמֶז כז)