The law which forbids breast-feeding after 2 years of age. To give you a Qur’anic reference:
And the mothers should suckle their children for two whole years for him who desires to make complete the time of suckling;… (2:233)
To give you a reference from a Sunni source (which clearly contradicts the creation of a ‘special case’):
Imam Malik’s Muwatta: Book 30, Number 30.1.11:
Yahya related to me from Malik that Yahya ibn Said said that he heard Said ibn al-Musayyab say, “Suckling is only while the child is in the cradle. If not, it does not cause flesh and blood relations.”
Yahya related to me from Malik from Ibn Shihab that he said, “Suckling however little or much, makes haram. Kinship by suckling makes men mahram.”
Yahya said that he had heard Malik say, “Suckling, however little or much when it is in the first two years, makes haram. As for what is after the first two years, little or much, it does not make anything haram. It is like food.”
Wa-alaykum assalam