Reference: Siyar A’laam an-Nubalaa – Volume 1, Page 461
‘Abdullaah ibn Mas’ood said:
When we had learnt ten aayahs [of the Qur.aan] from the Prophet (sal-Allaahu ‘alayhi wa sallam), we would not move on to the next ten [aayahs] which were revealed after them, until we had learnt what they contained of knowledge.