Selecciona el campo T.Cantidad con mayor valor

maxQuery.sql

SELECT MAX( T.Cantidad ) , T.civicrm_contribution_source
FROM (
    SELECT COUNT( * ) AS Cantidad, civicrm_contribution.source AS civicrm_contribution_source
    FROM civicrm_contact
         LEFT JOIN civicrm_contribution ON civicrm_contact.id = civicrm_contribution.contact_id
    WHERE civicrm_contact.id =8
    GROUP BY civicrm_contribution.source
    ORDER BY Cantidad DESC
) AS T