In hydrazine (N₂H₄) the hybridization of nitrogen is

The Lewis structure of N₂H₄ is

Every N atom has one lone pair of electrons and is bonded to three other atoms (one N and two H atoms). Thus, steric number of every N  is 3 + 1 = 4 . This implies that four hybrid orbitals are needed by every N which is possible only through sp³  hybridization.