Ruling on Fasting While Breastfeeding
Question

Is it permissible for my wife who is breastfeeding my ten-month-old son not to fast during Ramadan?
Praise be to Allah.With regard to breastfeeding mothers – and also pregnant women – two scenarios may apply: 
1- If the woman is not affected by fasting, and fasting is not too difficult for her, and she does not fear for her child, then she is obliged to fast, and it is not permissible for her not to fast. 
2- If the woman fears for herself or her child because of fasting , and fasting is difficult for her, then she is allowed not to fast, but she has to make up for the days that she does not fast. 
In this situation it is better for her not to fast , and it is makruh for her to fast. Some of the scholars stated that if she fears for her child, it is obligatory for her not to fast and it is haram for her to fast. 
Al-Mirdawi said in al-Insaf (7/382): 
“It is makruh for her to fast in this case… Ibn ‘Aqil said: If a pregnant woman or a breastfeeding mother fears for her pregnancy or her child, then it is not permissible for her to fast in this case, but if she does not fear for her child then it is not permissible for her not to fast.” 
Shaykh Ibn ‘Uthaymin (may Allah have mercy on him) was asked in Fatawa al-Siyam (p. 161): 
If a pregnant woman or breastfeeding mother does not fast with no excuse, and she is strong and in good health, and is not affected by fasting, what is the ruling on that? 
He replied: 
“It is not permissible for a pregnant woman or breastfeeding woman not to fast during the day in Ramadan unless they have an excuse. If they do not fast because they have an excuse, then they have to make up the missed fasts, because Allah says concerning one who is sick (interpretation of the meaning): 
“and whoever is ill or on a journey, the same number [of days which one did not observe Sawm (fasts) must be made up] from other days.” [al-Baqarah 2:185]
Pregnant women and breastfeeding mothers come under the same heading as those who are sick. If their excuse is that they fear for the child, then as well as making up for the missed fasts, according to some scholars they also have to feed one poor person for each day missed, giving wheat, rice, dates or any other staple food. 
Some of the scholars said that all they have to do is make up the missed fasts, no matter what the situation, because there is no evidence in the Quran or Sunnah for giving food in this case, and the basic principle is that there is no obligation unless proof of that is established. This is the view of Abu Hanهfah (may Allah have mercy on him) and it is a strong view.” 
Shaykh Ibn ‘Uthaymin (may Allah have mercy on him) was also asked in Fatawa al-Siyam (p. 162) about a pregnant woman who fears for herself or her child, and does not fast – what is the ruling? 
He replied by saying: 
“Our answer to this is that one of two scenarios must apply in the case of a pregnant woman. 
The first is if she is healthy and strong, and does not find fasting difficult, and it does not affect her fetus. In this case the woman is obliged to fast, because she has no excuse not to do so. 
The second is where the pregnant woman is not able to fast, either because the pregnancy is advanced or because she is physically weak, or for some other reason. In this case she should not fast, especially if her fetus is likely to be harmed, in which case it may be obligatory for her not to fast. If she does not fast, then like others who do not fast for a valid reason, she has to make up for the days when that excuse no longer applies. When she gives birth, she has to make up for those fasts after she becomes pure from nifas. But sometimes the excuse of pregnancy may be lifted but then immediately followed by another excuse, namely breastfeeding. The breastfeeding mother may need food and drink, especially during the long summer days when it is very hot. So she may need not to fast so that she can nourish her child with her milk. In this case we also say to her: Do not fast, and when this excuse no longer applies, then you should make up for the fasts that you have missed.” 
Shaykh Ibn Baz said in Majmu’ al-Fatawa (15/224): 
“With regard to pregnant women and breastfeeding mothers, it is proven in the hadith of Anas ibn Malik al-Ka’bi, narrated by Ahmad and the authors of al-Sunan with a sahih isnad, that the Prophet (peace and blessings of Allah be upon him) granted them a dispensation allowing them not to fast, and he regarded them as being like travelers. From this it is known that they may not fast but they have to make up the fasts later, just like travelers. The scholars stated that they are only allowed not to fast if fasting is too difficult for them, as in the case of one who is sick, or if they fear for their children. And Allah knows best.” 
It says in Fatawa al-Lajnah al-Daimah (10/226): 
“The pregnant woman is obliged to fast during her pregnancy, unless she fears that fasting may affect her or her fetus, in which case she is allowed not to fast, and she should make up the fasts after she gives birth and becomes pure from nifas.”
And Allah knows best.