iRule - Specific Source to Specific Node

Here is a very basic way of doing it.

when CLIENT_ACCEPTED {
    if { [IP::addr [IP::client_addr] equals 8.8.8.8] }{
        node 10.0.0.1
    }
}

Are you wanting to map multiple sources to multiple nodes? That would require a little more logic but can be accomplished with a data group with the value being the node you want a particular source to go to.

when CLIENT_ACCEPTED {
    if { [class match [IP::client_addr] equals source_dg] }{
        node [class lookup [IP::client_addr] source_dg]
    }
    else {
        pool default_pool
    }
}