Whatever is in the heavens and whatever is in the earth is Allah's; and whether you manifest what is in your minds or hide it, Allah will call you to account according to it; then He will forgive whom He pleases and chastise whom He pleases, and Allah has power over all things.
Al-Baqra Verse 284
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