Narrated by Aisha, may Allah be pleased with her, who said: The Messenger of Allah, peace and blessings be upon him, said: "One suckling does not make [a marriage] forbidden, nor do two sucklings." (1)

11 - Chapter: On giving a reward at the time of weaning

2064 - Abdullah ibn Muhammad al-Nufayli narrated to us, Abu Mu'awiyah narrated to us (h)
And Ibn al-'Ala' narrated to us, Ibn Idris narrated to us, from Hisham ibn 'Urwah, from his father, from Hajjaj ibn Hajjaj, from his father, who said: I said: O Messenger of Allah, what removes from me the obligation of fosterage? He said: "A ghurrah: a slave or a slave-girl." (2)

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(1) Its chain of transmission is authentic. Isma'il: he is Ibn Ibrahim al-Asadi, known as Ibn 'Ulayyah, and Ayyub: he is Ibn Abi Tamimah al-Sakhtiyani, and Ibn Abi Mulaykah: he is Abdullah ibn 'Ubaydullah al-Taymi.
It was also narrated by Muslim (1450), Ibn Majah (1941), al-Tirmidhi (1183), and al-Nasa'i in "al-Kubra" (5428) via multiple chains from Ayyub, with this chain of transmission. Al-Tirmidhi said: Hasan Sahih.
It was also narrated by al-Nasa'i (5427) via the route of Shu'bah, from Ayyub, from Ibn Abi Mulaykah, from Aisha. He omitted Abdullah ibn al-Zubayr from its chain, and Ibn Abi Mulaykah had also heard from Aisha, so perhaps he narrated it in both ways.
Al-Nasa'i also narrated in "al-Kubra" (5439) via the route of Abu al-Sha'tha' al-Muharibi, from Aisha, that the Prophet of Allah, peace and blessings be upon him, used to say: "One sip does not make [a marriage] forbidden, nor do two sips."
It is in "Musnad Ahmad" (24026) and (25812), and "Sahih Ibn Hibban" (4228).

(2) Its chain of transmission is likely to be considered hasan. Hajjaj ibn Hajjaj: he is Ibn Malik al-Aslami; none narrated from him except 'Urwah ibn al-Zubayr. Al-Bukhari mentioned him in "al-Tarikh al-Kabir" 12/371, and Abu Hatim in "al-Jarh wa al-Ta'dil" 3/157, and neither mentioned any criticism nor praise of him. Al-'Ijli declared him trustworthy, Ibn Hibban mentioned him in "al-Thiqat", and al-Hafiz al-Dhahabi said in "al-Mizan": Truthful, and al-Hafiz Ibn Hajar said in "al-Taqrib": Acceptable. =