Sahih Muslim
Sahih Muslim 838 b
Between every two calls, there is a prayer
Arabic hadith text
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 "
Translation
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)."