This link contains the full Cisco DHCP configuration guide.
http://www.cisco.com/c/en/us/td/docs/ios/12_2/ip/configuration/guide/fipr_c/1cfdhcp.html#wp1000999
You are looking for the "Configure Manual Bindings Section" and the command:
Router(config)# ip dhcp pool name
Router(dhcp-config)#host address [mask |/prefix-length]
Router(dhcp-config)#client-identifierunique-identifier
Router(dhcp-config)#hardware-addresshardware-address type
Router(dhcp-config)#client-name name