Volume 8 · Book 78 · Hadith 672
Narrated Al-Musaiyab: When the death of Abu Talib approached, Allah's Apostle came to him and said, "Say: La ilaha illallah, a word with which I will be able to defend you before Allah."
— Sahih Bukhari, Volume 8, Book 78: Oaths and Vows, Hadith #672