Abdullah b. Mughaffal reported Allah's Messenger (ﷺ) u saying
There Is between the two calls (Adhan and Iqama) a prayer. And he mentioned it three times, and at the third time he said: This applies to those who wish to do it.
This hadith has been narrated by Abdullah b. Mughaffal by another chain of transmitters, but with this variation that he (the Holy Prophet) said at the fourth time
" He who wishes (may do to)."