The author of IHYA states:-
It is Makrooh to indulge in sex during three nights of each month; the first, the last and fifteenth. It is said that Shaitaan is on the prowl on these nights. The undesirability of sex on these nights is narrated from Hazrat Ali, Hazrat Mulawiya and Hazrat Abu Huraiah (Radiyallahu-Anhum).
The author of RIFAATUL-MUSLIMEEN states that in addition to the above; Wednesday nights and the nights of the two Eids must also be avoided. Also the night where after a person intends to go on a journey on the next day should be avoided. Intercourse on these nights may have an undesirable effect on the off-spring.
It is reported in TIBBE-NABAWI that Rasulullah (Sallallahu-Alayhi-Wasallam) advised Hazrat Ali (Radiyallahu-Anhum) not to cohabit on the fifteenth night as the shayateen appear in large number on this night.
In a footnote of SHAMAIL-TIRMIZI it is stated that if the child is conceived during salah times (When the salah is neglected), the result will be a disobedient child.