1.Bf6!
The threat is Qd8+ and Rxd8#. Black must take the bishop as neither 1... Be7 or 1... Be6 works, because of 2.Bxc6+ bxc6 3.Qd8+
1...	Qxf6
2.Rhe1+	Be7
If 2... Be6 3.Qd7# or 2... Ne7 3.Qd8# or 2... Qe7 3.Bxc6+ bxc6 3.Qd8#
3.Bxc6+	Kf8
4.Qd8+!	Bxd8
5.Re8#
Nimzowich-Alapin (1912)