משנה אויף יהושע 15:11

Rabban Gamaliel had diagrams of the moon on a tablet [hung] on the wall of his upper chamber, and he used to show them to the unlearned and say, “Did it look like this or this?” It happened that two witnesses came and said, “We saw it in the morning in the east and in the evening in the west.” Rabbi Yohanan ben Nuri said: they are lying witnesses. When they came to Yavneh Rabban Gamaliel accepted them. On another occasion two witnesses came and said, “We saw it at its proper time, but on the night which should have been the new moon it was not seen,” and Rabban Gamaliel accepted their evidence. Rabbi Dosa ben Harkinas said: they are lying witnesses. How can they testify that a woman has given birth when on the next day her belly is between her teeth (swollen)? Rabbi Joshua to him: I see your argument.