allow traffic to VS based on the source IP fwded in the http get request

If you are looking for a whitelist iRule, then below iRule should work fine. You will need to create a datagroup, "Whitelist_IPs" in below example, with all the source IPs you want to allow access. So all http requests which match URL and source IP from whitelist will be allowed, others will get 403.

when HTTP_REQUEST {
    if { ([matchclass [string tolower [HTTP::host]] equals "www.sample1.com"]) and !([matchclass [IP::remote_addr] equals "Whitelist_IPs"]) } {
    HTTP::respond 403
    }
}