Where does the energy required for excitation of electrons in hybridization come from?

We're commonly taught that when atoms want to hybridize in for instance methane, an electron is excited from $2s$ to $2p$ to allow for four unpaired electrons, which is necessary for bonding.

Where does the energy for this excitation come from?

• If you are talking about the sp3 hybridization: there is no excitation involved... – Greg Aug 17 '16 at 5:03