There is nothing wrong with a man having sexual relations with his wife following the cessation of nifas (postpartum bleeding) even before the end of forty days, once she has performed ghusl (ritual bathing)—provided it is considered safe to do so from a medical point of view.
Sheikh Ahmad Kutty, a senior lecturer and Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states: “As reported in a number of hadiths, following child birth, women during the time of the Prophet (peace and blessings be upon him) were in the habit of setting aside forty days as the period of nifas (postpartum bleeding), during which time they refrained from performing salah (ritual Prayers), fasting, reciting the Qur’an, performing the ritual Tawaf, as well as having sexual intercourse. However, upon the conclusion of forty days, they used to resume all of the above once they had purified themselves through a complete ghusl (bath).
As many scholars have pointed out, the above report is simply intended to state the habit of women during the time of the Prophet (peace and blessings be upon him) in their experience of nifas. In other words, it is not in any way intended to set the upper limit of nifas at forty days, for nifas could very well extend beyond forty days; so scholars set the upper limit of nifas as sixty. If the bleeding stopped before that, women were considered eligible to resume normal relations following ghusl.
All of the above discussions, however, revolve around the specification of maximum period of nifas, but when it comes to the lower or minimum period of nifas, there is nothing in the sources to specify the same, and hence the preferred view among scholars is there is no lower limit for nifas; it could very well end in a day or even less. The only valid criterion to be relied upon in such case is to ask whether actual bleeding has stopped or not. If bleeding has stopped, then it can be established that the period of nifas has stopped.
Having said this, I must, however, point out that many scholars caution against engaging in sexual relations before the end of forty days, for one of two reasons: first, there could be a risk that bleeding will resume; secondly, sexual intercourse immediately following childbirth may have an adverse effect on the health of the woman, since she has no time to recuperate from the birth [and the cervix may still be dilated]. Though such concerns may be genuine and valid, ultimately the decision in this matter should be left to the couple themselves. So they are advised not to rush to engage in sexual relations immediately after the bleeding has stopped before forty days; rather they must wait until such time that they can ascertain that the bleeding will not resume and that it is considered medically safe to do so—following the advice of a medical professional.
In conclusion: There is nothing wrong for a man to engage in sexual relations with his wife following the cessation of nifas, even before the end of forty days, once she has performed ghusl—provided it is considered safe to do so from a medical point of view.”