SHAFAQNA – The Grand Ayatollah Sistani answered a question about the ruling for fasting for breastfeeding women in Ramadhan.
Question: What is the ruling for a woman who breastfeeds in the month of Ramadhan?
The Grand Ayatollah Sistani: A woman who breastfeeds a child whether she is the mother of the child or a wet nurse, and her milk is not enough, if fasting is harmful for her or the child, fasting is not Wajib for her; and must feed the poor equal to (750 grams of bread, or pasta or flour) for every day (of fasting missed), and must fast days missed (some other time). But according to Wajib precaution, this ruling is for when breastfeeding is the only way of feeding the child, and if there is another way, for example can use powdered milk, according to Wajib precaution must fast.
Source: PERSIAN SHAFAQNA