Chess diagram

White to move.

1. Nd4+ Kc5
2. Kh1  

Zugzwang. The bishop is forked no matter where it moves. Or

1. … Kb7
2. Kxh2 Ka6
3. Nb3 Bf4+
4. Kh3 Kb5
5. Kg4 Bb8
6. f4 Kb4
7. f5  

Source: Endgame Study p.101, Hastings and St. Leonards Post