VERILY, this Qur'an shows the way to all that is most uprightand gives the believers who do good deeds the glad tiding that theirs will be a great reward;
Al-Isra (The Journey by Night) Verse 9
The Prophet used to take care of us in preaching by selecting a suitable time, so that we might not get bored. (He abstained from pestering us with sermons and knowledge all the time).
Sahih Bukhari: Volume 1, Book 3, Number 68