Musnad Abu Ya'la al-Mawsili 152:69

On the authority of Abu Wa'il, who said: Abdullah used to remind the people every Thursday. A man said to him, "O Abu Abd al-Rahman, if only you would remind us every day." He said, "As for that, what prevents me from doing so is that I dislike to make you bored. I seek the appropriate times for you with the exhortation, just as the Messenger of Allah (peace and blessings of Allah be upon him) used to seek the appropriate times for us with the exhortation during the days, for fear of weariness upon us."