عن أبي العالية قال : كان أبي صاحب عبادة ، فلما احتاج الناس إليه ، ترك العبادة وجلس للقوم 

On Authority of Abī Ā’liyah

Ubayy ibn K’ab used to be a person of  worship, and when the people were in need of him (due to his knowledge and high position amongst the companions) he would leave worship and sit with the people. (to answer their questions).

 [Siyar ‘Alām An-Nubalā Volume 3, page 399].

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• • The noble Companion of the Messenger of Allah – from the Ansār and those who partook in the Battle of Badr.
• • He was from the few who had memorised the whole Qur’ān in the lifetime of the Prophet – sallallāhu alayhi wa sallam -whom he ordered the people to take the Qur’ān from.
• • The Messenger of Allah said to him, “O Abā Mundhir (Ubay)! Do you know which verse from the Book of Allah – (you have memorised) with you – is the greatest?” He (Ubay) said, “Allah and His Messenger know best”. The Prophet (repeated and) said, “O Aba Mundhir (Ubay)! Do you know which verse from the Book of Allah – (you have memorised) with you – is the greatest?”. He (Ubay) said, “Allāhu laa ilāha illa huwal-Hayyul-Qayyoom … (āyatul-Kursi).He (Ubay) said, “He (The Prophet) then struck me on my chest and said “By Allah, may you be blessed in your knowledge O Aba Mundhir.” [Muslim, hadith no.810
• • On another occasion, the Prophet said to Ubay ibn K’ab, “Indeed Allah has commanded me to read the Qur’aan to you. He (Ubay) said, “Did He mention me by name?” He (the Prophet) said, “yes”. He (Ubay) said, “I was mentioned by the Lord of the Worlds?!” He said, “yes”. So Ubay began to shed tears. [Al-Bukhaari, hadith no.4961 and Muslim, hadith no. 799].