1. DEFINITION OF NIFAS
Nifas literally means "childbed, childbirth, parturition." In the Islamic legal terminology, it means "the blood which is discharged from a woman's womb during or after the childbirth." The blood discharged during the travail is not regarded as nifas.
In the present context the word nifas is usually translated as "post‑natal bleeding." The woman who has nifas is known as nafsa'.
The blood which is discharged from a woman's womb after a miscarriage is also nifas.
There is no minimum duration for nifas. Even if only a drop of blood is discharged during or after childbirth, it will be regarded as nifas.
As far as the period of occurance is concerned, any blood which is discharged within ten days of childbirth is nifas. So if a woman who saw no blood during or after the childbirth sees blood nine days later, that blood will still be regarded as nifas.
The maximum duration of nifas is ten days from the time of completion of childbirth or from the commencement of the bleeding. So if a woman sees blood at childbirth and it continues for ten days, all those days will be nifas. On the other hand, if a woman sees blood on the seventh day after the childbirth and it continues for ten days, then up to the end of the tenth day from
the childbirth she will consider herself in nifas; and for the remaining period (i.e., up to 17th day from the childbirth) she will act on precaution ‑ avoiding all things forbidden to a nafsa', and doing all that is required of a mustahadah.
When it is said "from the time of childbirth", it means after the "complete" delivery of the child.
There is no minimum duration between two nifas. For example, a woman who gave birth to twins who were born at five days interval, sees blood for 5 days after the first child and then it stops, and again she sees blood after the second child's birth ‑ then the two bleedings will be counted as two separate nifas.
2. THREE TYPES OF NAFSA'
1. A woman whose post‑natal bleeding does not exceed ten days. In such a case all the days of bleeding will be considered nifas.
2. A woman whose post‑natal bleeding exceeds ten days and, as far as her menstrual cycles are concerned, she is a zatu 'l‑'adah with a fixed number of days. In this case the days equal to the duration of her menstruation will be regarded as nifasand the remaining days as istihazah.
3. A woman whose post‑natal bleeding exceeds ten days and she is not a zatu 'l‑'adah. In this case she should look at the duration of her relatives' menstruation and then consider the same number of days as her nifas. If the duration of her relatives' menses is less than ten, then (a) she should count those days as nifas and (b) after that she should act on precaution up to the tenth day.
3. SOME GENERAL RULES
A nafsa’sees blood on the first day of the childbirth and then it stops and then again it starts on or before the tenth day. In this case there are two possibilites:
(a) The second bleeding does not exceed the tenth day from the commencement of the first flow‑both the flows and the pause between them will be regarded as one nifas. Of course, it is precautionarily better to act on precaution during the pause.
(b) The second bleeding exceeds the tenth day from the commencement of the first flow. This again has four possibilities:‑
i. The woman has a fixed number of days for her menstrual cycles, and the second flow took place within the fixed number: For example, her menses usually continues for seven days; now she saw blood of nifas for two days from the childbirth, then it stopped, and re‑started again on the sixth day and continued exceeding the tenth day. Then the first flow, the pause and the second bleeding within the fixed number (i.e, upto the seventh day after childbirth), will be regarded as one nifas and the remaining days will be istihazah.
ii. The woman has a fixed duration for her menstrual cycles, but the second flow did not take place during the fixed duration ‑ then the first flow will be nifas, the pause will be regarded as a period of purity and the second flow will be regarded as istihazah.
iii. The woman does not have a fixed pattern for her menstrual cycles, and the second flow started during the fixed duration of her relatives' monthly periods ‑ then the days equal to the duration of her relatives' monthly periods will be nifasand the remaining istihazah. Of course, if the duration of her relatives' periods is less than ten days then she should act on precaution after the last day up to the tenth day.
iv. The woman does not have a fixed pattern for her menstrual cycles, and the second flow started after the fixed duration of her relatives' monthly periods ‑ then the first flow will be nifas; and during the pause and the second flow she should act on precaution up to the tenth day.
When the nifas stops but the nafsa’is uncertain whether or not it has stopped completely, then she should examine herself just as a hayz was required to do in similar circumstances. (See page 13 for details.)
4. PRE‑NATAL BLEEDING
As mentioned in part one, it is possible for a pregnant woman to have menstruation.
Salman al‑Farsi asked Imam 'Ali (peace be upon him) about the sustenance of a child in its mother's womb. The Imam said, "Allah, subhanahu wa ta'ala, preserves the (blood of) menstruation for him and makes it into his sustenance in his mother's womb." Sulayman bin Khdlid asked Imam Ja'far as‑Sadiq that, "Does a pregnant woman have her monthly period sometimes?" The Imam said, "Yes; and that is because the food of a child in the womb of its mother is the blood. Sometimes the blood is in abundance and is in excess (to his need); and when it is in excess, it is shed out; and when it is shed out (she is regarded as a ha’iz and) she is not allowed to perform salat. " 
In this chapter we shall discuss the nature of the blood seen during pregnancy.
If a pregnant woman sees blood and she is sure that it is the menstrual flow, then she should consider it as menstruation.
But if she does not know whether it is hayz or istihazah, then there may be three possibilites:‑
(1) The discharge has the three signs of hayz and it came during or aroung the fixed number of days, then she should consider it as hayz.
(2) The discharge does not have the three signs nor did it come during or around the fixed number of days, then she should consider it as istihazah.
(3) The discharge has the three, signs but it did not come during or around the fixed number of days or vice verse, then she should act on precaution.
If a pregnant woman sees blood just a few days before the childbirth, then there are four possibilities:
(1) The bleeding continues up to the child birth and she knows that it is menstruation and it has the three signs, then it will be regarded as menstruation.
(2) The bleeding continues up to the childbirth but she does not know that it is menstruation ‑ then if it has the three signs or it occured during the fixed time of her menses, it is hayz; otherwise it will be considered as istihazah.
(3) The bleeding stopped ten days before the childbirth ‑ then if it has the three signs, it will be regarded as menstruation; otherwise it is istihazah.
(4) The bleeding stopped during the ten days prior to the childbirth ‑ then if it has the three signs or it occured during the fixed time, it will be regarded as menstruation; otherwise it will be considered as istihazah.
5. THE THINGS FORBIDDEN TO THE NAFSA'
The things which were fobidden to the hayz are also forbidden to the nafsa'.
She is forbidden from touching the Qur'an. Staying in a mosque or putting something in it is not allowed to her; passing through a mosque is only allowed if she enters from one door and without stopping goes out of another. But she cannot even pass through the Sacred Mosque of Mecca and the Prophet's Mosque at Medina. She cannot recite the verses of sajdah. And sexual intercourse with her is forbidden.
She is also excused from salat. Like a hayz, she is not even required to perform them as qaza. She is also exempted from fasting, but in this case she has to fast afterwards as qaza.
6. GHUSL U'N‑NIFAS
When a woman becomes pure from nifas, it is wajib for her to perform ghusl. Apart from sexual intercourse, all the acts forbidden to her will remain so until she performs ghuslu 'n‑nifas.
The manner of performing ghuslu 'n‑nifas is same as explained in part one of this book.
 al‑'Amili, op. cit., vol. 2, p. 579