Hadith 21:71
Sahih (Darussalam)
Something similar was narrated from Umm 'Atiyyah except, that he (the narrator) said:
"Three times or five, or seven, or more than that, if you think that (is necessary)."
أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا حَمَّادٌ، عَنْ أَيُّوبَ، عَنْ حَفْصَةَ، عَنْ أُمِّ عَطِيَّةَ، نَحْوَهُ غَيْرَ أَنَّهُ قَالَ " ثَلاَثًا أَوْ خَمْسًا أَوْ سَبْعًا أَوْ أَكْثَرَ مِنْ ذَلِكِ إِنْ رَأَيْتُنَّ ذَلِكِ "
Original Reference: Sunan an-Nasa'i 1888