What is the concept of adult suckling (rada' al-kabir), and is it permissible for it to occur through direct suckling from the breast of a foreign woman or a mahram?

There is no benefit in seeking a weak probability as long as the matter can be interpreted in a way that is legally permissible. Narrations have been reported from Ibn Sa'd, Abu 'Amr, and Ibn Qutaybah clarifying that the suckling of an adult occurs by drinking expressed milk, not by direct suckling from the breast, because that is not permissible in Islamic law, and it is not lawful for Salim to look at her breast.