מדרש על בראשית 6:18

'You, and your wife, etc.' (Gen. 8:16) Rabbi Yudan ben Rabbi Simon, and Rabbi Yochanan in the name of Rabbi Shmuel ben Rabbi Itzchak said: As soon as Noach entered the Ark, cohabitation was forbidden to him, that's why it is written: 'And you shall come into the ark, you, and your sons' (Gen. 6:18) - apart; 'and your wife, and your sons’ wives' - apart. When he went out, God permitted it to him, as it is written: 'Go forth from the Ark, you and your wife'. Rabbi Aivu said: 'They are lonely in want and famine' (Job 30:3) - when want and famine visit the world, regard your wife as though she were lonely [i.e. monstrous]. R. Huna said: it is written 'and to Yosef were born two sons' (Gen. 41:50) - when? 'Before the year of famine came' (Gen. 41:50).