What are the conditions for a just witness in marriage according to Imam Al-Shafi'i?

For the validity of a witness in marriage, the following conditions are stipulated: Islam, sanity, masculinity, puberty, and uprightness (adalah). This is the view of the majority of jurists, including Imam Al-Shafi'i, based on the saying of the Prophet, peace and blessings be upon him: "There is no marriage except with a guardian and two upright witnesses."