Al-Matalib al-'Aliyah 771 — The states of the dying person

It is narrated from Sayyiduna Anas bin Malik (may Allah be pleased with him) that Sayyiduna Abu Bakr al-Siddiq (may Allah be pleased with him) came to the Prophet (peace and blessings be upon him) while he was extremely grieved and sad. He (peace and blessings be upon him) asked: "What is the matter, that I see you so sorrowful?" He said: "O Messenger of Allah! Last night I was with a certain cousin of mine while he was in the throes of death, struggling with his soul." He (peace and blessings be upon him) said: "Then why did you not prompt him to say 'La ilaha illallah' (there is no god worthy of worship except Allah)?" He said: "O Messenger of Allah! I did so." He (peace and blessings be upon him) asked: "Did he say this word?" He said: "Yes." He (peace and blessings be upon him) said: "Then Paradise has become obligatory for him." Sayyiduna Abu Bakr (may Allah be pleased with him) said: "O Messenger of Allah! What is the standing of this word for the living?" He (peace and blessings be upon him) said: "It is far more effective in erasing and demolishing their sins; it uproots their sins entirely."
Musnad Abi Ya'la: 771. Its chain contains Za'idah bin Abi al-Ruqad and Ziyad al-Numayri, because of whom there is weakness in the chain; however, other sahih hadith on the virtue of the word of Tawhid exist as supporting reports.