Markandeyapurana 31.33

31.33

retomūtrakṛtāhārāstanmāsaṃ pitarastayoḥ /
tasmāttu prathamaṃ kāryaṃ prājñenopanimantraṇam //

“And both he, who shall perform a śrāddha that ought to be performed by those self-controlling men, and he, who indulges in sexual intercourse after having offered the śrāddha and eaten the food,—the ancestors of these two men verily lie down in that semen a month. Moreover he who eats at a śraddha and he who goes to a śrāddha after intercourse with a woman,—the ancestors of those two men feed on semen and urine for that month. Therefore a wise man must first issue an invitation; and men who have intercourse with women before the day arrives must be shunned.