Mobile Ad hoc Networks (MANETs) are open to a wide range of attacks due to their unique characteristics such as dynamic topology, open medium, absence of infrastructure, multi hop scenario and resource constraint. An ad hoc node in mobile ad hoc networks operates as not only end terminal but also as an intermediate router. In this way, multi-hop scenario occurs in MANETs. This multi hop scenario demands security against malicious behavior, because there may be one or more attackers in the route from source to destination. A routing protocol in MANETs is said to be securing that detects the detrimental effects of malicious node. Many security solutions for ad hoc routing have been proposed. But still many attacks are not addressable by these protocols. In this paper, we have proposed a protocol to secure the source routing in MANETs that allows both communicating parties as well as intermediate nodes to authenticate other nodes.