Sheikh Muhammad b. `Abd Allah al-Mijlî, presiding judge at the Mecca District Court
A nursing mother who finds fasting in Ramadan difficult for her is fully within her rights to abstain from fasting.
A pregnant woman and a nursing mother, if they break their fasts on account of their condition, take the same ruling as those who break their fasts because they are ill or on a journey. This means that they must make up the missed fasts at a later date, when doing so becomes easy for them.
There have been a few scholars who held the opinion that pregnant women and nursing mothers can simply opt to expiate for the missed days by feeding a poor person for each day missed. However, this opinion is not a strong one.
The correct ruling is that these women have to make up the fasts that they miss. Allah says: “Whoever among you who is ill or on a journey should fast a number of other days.” [Sûrah al-Baqarah: 184]
The application of this ruling to pregnant women and nursing mothers is made clear in the following hadîth.
Anas b. Mâlik relates that the Prophet (peace be upon him) said: “Allah has excused the traveler from the obligation to fast and from half the units of his prayer. He has excused the pregnant woman and the nursing mother from fasting.” [Sunan al-Tirmidhî (715), Sunan Abî Dâwûd (2408), and Sunan Ibn Mâjah (1667)]
This indicates to us that the ruling for the traveler being excused from fasting is the same as that of a nursing mother. Since the traveler must make up his fast later on, so must the nursing mother.
And Allah knows best.
Source: Islam Today