Function quote_send_request_with_source 

pub fn quote_send_request_with_source(
    state: &AccountState,
    destination: &str,
    client_id: &str,
    created_at: u32,
    content: &str,
    source: Option<&str>,
) -> Result<Vec<u8>>

Outgoing source belongs to this reply; embedded reference source stays in XML.