Sucking a Woman's Breasts

Q: Prohibitions and Permissions-27: In the heat of passion, Umar sucks at the nipples of his wife. Is this permissible when she has no milk in her breasts? Will the marriage be invalidated if he does so at a time when she does have milk?

Answer: There is no sin in sucking at the nipples when in the throes of passion, but it is Haraam to drink the milk. However, this will not make her his suckling mother in any way because his period of suckling is over.

Fatawa Rahimiyyah vol.3