This is a long hadith about when to have and not have intercourse and the effects if a child is conceived at that time and so on.
It is narrated by Abu Saeed Khudri that the Messenger of Allah (S) advised Imam Ali (a):
O Ali, when the bride arrives, take off her shoes; then wash her feet and sprinkle the water from the door till the rear wall of the house as this would remove seventy thousand types of troubles, seventy thousand types of blessings would enter, seventy thousand types of blessings would descend on you and that bride. Its blessing will reach every corner of the house and as long as the bride remains in that house, she would be secure from dandruff, leprosy, and insanity.
O Ali, do not allow that bride to consume milk, vinegar, coriander and sour apples for seven days.
Amirul Momineen (a) asked: O Messenger of Allah (s), what is the reason for that?
He replied: These things make the womb sterile and she remains barren. O Ali, a sack lying in some comer of the house is better than a woman, who cannot produce children.
Then he said: O Ali, do not become intimate with your wife during the beginning, middle, and end of the month, as she and her issues would be prone to insanity, dandruff, and leprosy.
O Ali, do not have intercourse after the noon prayer, as the issue born of that union, will remain in distress.
O Ali, do not speak during the act; if a child is born, it might have a speaking disability. And one should not glance at the female genitals during intercourse; he should keep his eyes closed as it might cause the issue to be born with a visual handicap.
O Ali, don’t have intercourse with your wife when you are aroused by looking at some other woman, as the child born of that union will be eunuch or insane.
O Ali, if one sleeps in the bed of his wife in the condition of sexual impurity, he should not recite the Holy Quran, as I dread that fire may descend from the heavens and burn down both of them.
O Ali, before intercourse, keep a napkin ready for yourself and a napkin for your wife. Both of you must not use the same napkin as it, first of all, creates enmity between the partners finally leading to separation.
O Ali, do not have intercourse in the standing position, as it is an act of donkeys; if a child is born, it would wet the bed like donkeys.
O Ali. Do not have intercourse on the eve of Eidul Fitr; If a child is born of that union. Many evils will be seen will be seen him.
O Ali. Do not have intercourse on the eve of Eid of sacrifice; If a child is born of that union it will have six or four fingers in its hand.
O Ali, do not have intercourse under a fruit-bearing tree. If a child is born of that union, it would be either a killer or a leader of oppressors.
O Ali, do not have intercourse in front of the sun. without drawing a curtain; because the child is born of that union would remain in poverty and distress as long as he lives.
O Ali, do not have intercourse between Adhan and Iqamah; if a child is born of that union, it would be inclined to bloodshed.
O Ali, do not have intercourse without ablution when the wife is pregnant otherwise, the child born will be hard-hearted and miser.
O Ali, do not have intercourse on 15th of Shaban; if a child is born of that union, it would be niggardly and the mark of blackness shall be present on its face.
O Ali, do not have intercourse at the end of the month of Shaban; if a child is born of that union, it would be a robber and killer and many would be killed at his hands.
O Ali, do not have intercourse on the terrace; if a child is born of that union, he would be a hypocrite, ostentatious person or heretic.
O Ali, do not have intercourse on the night preceding the morning when you set out on a journey; if a child is born of that union, he would become a squandered and the squanderers are brothers of Satan. And if you are going on a journey of three days duration; if a child is born of that union, it will be an oppressor.
O Ali, have intercourse on Monday eve; if a child is born of that union, it would be a memorizer (hafidh) of Quran and will be thankful for divine blessings.
O Ali, if you have intercourse on Tuesday eve, the child born of that union would,
in addition to getting the good fortune of Islam, will also get the status of martyrdom. His mouth will be fragrant, he would be merciful, generous and devoid of backbiting, rumor mongering and false allegation.
O Ali, if you have intercourse on Thursday eve, the child born of that union would either be a religious jurisprudent or a scholar. And if you have intercourse at midday on Thursday, the satan will not have access to him until his last moments and the Almighty Allah will bestow him with the well being of religion and the world.
O Ali, if you have intercourse on Friday eve, the child born of that union would be famous for his oratory and eloquence and no speaker will not be able to equal him.
O Ali, if you have intercourse on Friday afternoon (Asr), the child born out that union would be considered among the intellectuals ofthe time. If you have intercourse on Friday eve, after the Night Prayer (Isha), it is expected that the child born of that union will be included among the mystic pivots (Abdaal).
O Ali, do not have intercourse in the first part of the night (early evening); because a child born of that union might become a sorcerer, and might prefer the world over the hereafter.
O Ali, learn these pieces of advice from me like I learned them from Jibraeel.
(Source: Hilyat al Muttaqin page 112-114)