Thuwayba was the slave of Abu Lahab ibn ‘Abd al-Muttalib, the uncle of Muhammad.
There is a tradition that Thuwayba was freed when Mohammad was born:
On the day the Prophet (peace be upon him) was born, Thuwayba rushed to her master Abu Lahab in joy and said, “Have you heard?! Aminah has just given birth to a son, for your brother Abdullah!” As was the custom of Arabs to show generosity at receiving good news, and since this was the newborn son (peace be upon him) of his recently deceased brother, Abu Lahab gestured with his thumb and forefinger, saying to Thuwayba, “Go, for you are free.” For this, his punishment in the Hereafter is lessened by a small sip of water equal to what could be held in the small curve of flesh at the base of the thumb till the forefinger. (Mussanaf of ‘Abdur-Razzaq)
This is reinforced by another hadith:
Narrated ‘Ursa; Thuwaiba was the freed slave girl of Abu Lahb whom he had manumitted, and then she suckled the Prophet. When Abu Lahb died, one of his relatives saw him in a dream in a very bad state and asked him, “What have you encountered?” Abu Lahb said, “I have not found any rest since I left you, except that I have been given water to drink in this (the space between his thumb and other fingers) and that is because of my manumitting Thuwaiba.” (Sahih Bukhari 62:38)
There are competing traditions that Thuwayba was freed either before Muhammad was born or at the time of the Hijrah. These seem more realistic, but understandably, Islamic scholars prefer the tradition that she was freed after giving news of Muhammad’s birth.
Thuwayba also suckled Abu Salama and Hamzah ibn ‘Abd al-Muttalib, who was said to be four years older than Muhammad. Her own son was Masrah. Hazmah can be four years older than and also Muhammad’s milk brother if he was suckled when Thuwayba had a different child–early Islamic scholars speculated that Hazmah could have only been two years older than Muhammad if Thuwayba suckled both, but I don’t see why she couldn’t have had an earlier child who died young or is simply not recorded.
Thuwayba is held to be an early convert to Islam.
She accompanied Muhammad at the time of the Hijrah.
She died in AH 7.