This article tells us the following story about R' Yishmael ben Elisha and his mother:
Rabbi Ishmael's mother was a very pious woman, and she worshipped her son. But one day she astonished the Sages when she appeared before them to complain about her son. Said she, "Rebuke my son, Ishmael, for he does not show me honor." The faces of the Sages turned pale, and they asked her, "Is it possible that Rabbi Ishmael should not show honor to his mother? What has he done to you?" She replied, "Before he goes to the Beth Hamidrash, I want to wash his feet, and to drink the water with which I have washed them, but he will not permit it!" Then the Sages said to Rabbi Ishmael, "Since this is her wish, honor her by permitting it.
What is the source for this story?