Verily, those who have attained to faith and do good works, and are constant in prayer, and dispense charity - they shall have their reward with their Sustainer, and no fear need they have, and neither shall they grieve.
Al-Baqara (The Cow) Verse 277
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