Odd number of stones are to be used for cleaning (the private parts after answering the call of nature), and casting of pebbles at the Jamras is to be done by odd numbers (seven), and (the number) of circuits between al-Safa' and al-Marwa is also odd (seven), and the number of circuits (around the Ka'ba) is also odd (seven). Whenever any one of you is required to use stones (for cleaning the private parts) he should use odd number of stones (three, five or seven).  

قَالَ رَسُولُ اللَّهِ ﷺ الاِسْتِجْمَارُ تَوٌّ وَرَمْىُ الْجِمَارِ تَوٌّ وَالسَّعْىُ بَيْنَ الصَّفَا وَالْمَرْوَةِ تَوٌّ وَالطَّوَافُ تَوٌّ وَإِذَا اسْتَجْمَرَ أَحَدُكُمْ فَلْيَسْتَجْمِرْ بِتَوٍّ  

[Machine] The Messenger of Allah, ﷺ , said that "al-Istijmar" is a purification method, and "al-Ramy" (stoning the pillars) is a purification method, and the "Sa'y" (walking) between Safa and Marwa is a purification method, and "Tawaf" (circumambulation) is a purification method. And when one of you performs "al-Istijmar", then let him perform it with a "Taww" (an odd number of stones), as stated by Al-Ruzbary in his narration. And "al-Taww" is the "Witr" (an odd number).  

قَالَ رَسُولُ اللهِ ﷺ الِاسْتِجْمَارُ تَوٌّ وَرَمْيُ الْجِمَارِ تَوٌّ وَالسَّعْيُ بَيْنَ الصَّفَا وَالْمَرْوَةِ تَوٌّ وَالطَّوَافُ تَوٌّ وَإِذَا اسْتَجْمَرَ أَحَدُكُمْ فَلْيَسْتَجْمِرْ بِتَوٍّ لَفْظُهُمَا سَوَاءٌ زَادَ الرُّوذْبَارِيُّ فِي رِوَايَتِهِ وَالتَّوُّ الْوِتْرُ