Between every two calls, there is a prayer
وَحَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا عَبْدُ الأَعْلَى، عَنِ الْجُرَيْرِيِّ، عَنْ عَبْدِ اللَّهِ، بْنِ بُرَيْدَةَ عَنْ عَبْدِ اللَّهِ بْنِ مُغَفَّلٍ، عَنِ النَّبِيِّ صلى الله عليه وسلم . مِثْلَهُ إِلاَّ أَنَّهُ قَالَ فِي الرَّابِعَةِ " لِمَنْ شَاءَ " .
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)."