Which Quranic ayat state the number of Imams is 12?

While discussing the no. of imams with a friend of a different sect, we had this friendly argument. She says that the no of Imams are not clearly mentioned in the Holy Qur'an. Whereas, I for sure know it is and the number is 12. I'm looking for the sura and ayat no. (And the translation too, if possible) which confirms the existence of the 12 Imams. Which Quranic ayat state the number of Imams is 12?