Śatapatha Brāhmaṇa ("of a hundred paths") 4.6.7.10

4.6.7.10

evamevaitaddhavirdhānam pariśrayanti | etasmai mithunāya tira ivedam mithunaṃ caryātā iti vyṛddhaṃ vā etanmithunaṃ yadanyaḥ paśyati tasmādyadyapi jāyāpatī mithunaṃ carantau paśyanti vyeva dravata āga eva kurvāte tasmādadvāreṇa havirdhānam prekṣamāṇam brūyānmā prekṣathā iti yathā ha mithunaṃ caryamāṇam paśyedevaṃ tatkāmaṃ dvāreṇa devakṛtaṃ hi dvāram

In like manner they enclose the Havirdhâna on all sides with a view to that generation, thinking, 'Quite secretly this generation shall be carried on!' for improper, indeed, is the generation which another sees: hence even when a husband and wife are seen, while carrying on intercourse, they run away from each other, for they give offence. Therefore to any one looking into the Havirdhâna, except through the door, let him say, 'Look not!' for it is as if he were seeing intercourse being carried on. Freely (one may look) through the door, for the door is made by the gods.