Among his outstanding traits (radhiallahu ‘anhu) is what Al-Bukhari and Muslim collected on the authority of Anas bin Malik (radhiallahu ‘anhu) that Allah’s Messenger (sallallahu ‘alayhi wa sallam) said to Ubay,
إِنَّ اللهَ أَمَـرَنِـي أَنْ أَقْـرَأَ عَـلَـيْـكَ , قَـالَ : آلله سَـمَّـانِـي لَـكَ ؟ قَـالَ : اللهُ سَـمَّـاكَ لِـي . قَـالَ : فَـجَـعَـلَ أُبَـيٌّ يَـبْـكِـي .
“Indeed Allah ordered me to teach you” He (i.e. Ubay) said, “Did Allah mention my name to you?” the Prophet said, “Allah mentioned your name to me” Anas bin Malik said, “Ubay began to weep.”
Likewise you should contemplate in order to grasp Ubay’s the full extent of understanding of the religion (radhiallahu ‘anhu); his response to this question wasn’t after long period of time like a week or a month in which he could review the verses and contemplate its meanings; rather he (radhiallahu ‘anhu) merely responded immediately after the Messenger (sallallahu ‘alayhi wa sallam) repeated the question; so he chose this blessed verse.