If the question pertains to whether using a milk pump affects ablution (wudu), there is no issue with that. A person can pray with the ablution they had before using the pump. However, if the question is about continuing to milk during the prayer, it is generally considered inappropriate. Although modern milk pumps are portable and may not be felt by the mother, it is still recommended to avoid engaging in this activity during prayer.
In Islam, performing a lot of actions (known as amel-i kesir) during prayer—whether through the individual’s own actions or external interference—can invalidate the prayer. Since milking typically involves ongoing movement, it can disrupt the prayer and thus render it invalid. Therefore, unless no other alternative is available, it is better to milk outside of prayer times.