Sahih Bukhari Volume 001, Book 003, Hadith Number 070.
Narated By Abu Wail : 'Abdullah used to give a religious talk to the people on every Thursday. Once a man said, "O Aba 'Abdur-Rahman! (By Allah) I wish if you could preach us daily." He replied, "The only thing which prevents me from doing so, is that I hate to bore you, and no doubt I take care of you in preaching by selecting a suitable time just as the Prophet used to do with us, for fear of making us bored."