Is the phrase "prayer is gathering" said once, or is it repeated when calling for the eclipse prayer, and how often is it repeated if its repetition is legislated?

The Prophet, peace and blessings be upon him, commanded to call for the Eclipse Prayer by saying: "As-salatu jami'ah (Prayer is gathering)." The Sunnah is to repeat this call until the caller believes he has made the people hear, without specifying a number of times.