ת"ר אדם נברא בערב שבת ומפני מה שלא יהו המינים אומרים שותף היה לו להקדוש ברוך הוא במעשה בראשית דבר אחר שאם תזוח דעתו עליו אומר לו יתוש קדמך במעשה בראשית דבר אחר כדי שיכנס למצוה מיד
The Sages taught in a baraita (Tosefta 8:7): Adam the first man was created on Shabbat eve at the close of the six days of Creation. And for what reason was this so? So that the heretics will not be able to say that the Holy One, Blessed be He, had a partner, i.e., Adam, in the acts of Creation. Alternatively, he was created on Shabbat eve so that if a person becomes haughty, God can say to him: The mosquito preceded you in the acts of Creation, as you were created last. Alternatively, he was created on Shabbat eve in order that he enter into the mitzva of observing Shabbat immediately.