Hadith 1888
Chapter 34: Washing the Deceased more than seven times - كتاب الجنائز
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 " .
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)."
Reference : Sunan an-Nasa'i 1888
In-book reference : Book 21, Hadith 71