How is the brotherhood of suckling proven? Is the testimony of one woman or the wet nurse herself sufficient, or is suckling only proven by the usual evidentiary witnesses? And what is the number of sucklings that necessitate prohibition?

The testimony of a single woman regarding suckling (رضاع) is accepted if she is reliable (مرضية), based on what Al-Bukhari and Muslim narrated from Uqbah ibn Al-Harith: "that he married Umm Yahya, daughter of Abu Ihāb. Then a black female slave came and said: 'I suckled both of you.' So I went to the Prophet, peace and blessings be upon him, and mentioned that to him. He said: 'How can you (marry her) when she claims that she suckled both of you?' So he forbade him from her." Ibn Qudamah said: "This indicates the sufficiency of a single woman, and this was the practice during the time of Uthman, may Allah be pleased with him, and thereafter."