Is a declaration of impregnation of a female slave by a sick person valid?

Primary text

The declaration made by a sick person regarding the impregnation of a female slave is valid because he possesses the right to do so, thus possessing the right to declare it. Similarly, he possesses the right to declare anything he owns. If he makes such a declaration and then dies, and it is established that he impregnated her while she was in his possession, her child is free by origin (hurr al-asl), and the mother becomes an 'Umm Walad' (mother of a child by her master), and she is freed from the principal wealth (al-ra's al-mal).