Source: Fatawa Aman Puri by Sheikh Ghulam Mustafa Zahir Aman Puri
Question:
Is breastfeeding established by the testimony of one woman or not?
Answer:
If the breastfeeding woman gives testimony alone, then this testimony is accepted, and breastfeeding will be established.
❀ Sayyidina Uqbah bin Harith (may Allah be pleased with him) narrates:
"I married the daughter of Abu Wahab, and a black woman came and said: I have breastfed both of you. I asked the Prophet Muhammad (peace be upon him) about this, and he turned away from me. I asked again, and he turned away again. The third or fourth time he said: When this has been said, how can she remain with you? So he prohibited her from (staying with his wife)."
Reference: (Sahih Bukhari: 2659)