The Prophet (ﷺ) said: The testimony of a nomad Arab against a townsman is not allowable.
Sunan Abi Dawud Book 25, Hadith 32
← Previous Hadith The Messenger of Allah (ﷺ) said: The testimony of a deceitful man or woman, of an adulterer and adulteress, and of one who harbours rancour against his brother is not allowable.

Sunan Abi Dawud Book 25, Hadith 31 Next Hadith → "I married Umm Yahya daughter of Abu Ihab. A black woman entered upon us. She said that she had suckled both of us. So I came to the Prophet (ﷺ), and amentioned it to him. He turned away from me. I said (to him): Messenger of Allah! she is a liar. He said: What do you know? She has said what she has said. Separate yourself from her (wife).

Sunan Abi Dawud Book 25, Hadith 33