كتاب الشروط
Chapter: The conditions permissible on embracing Islam, and in contracts and transactions
باب مَا يَجُوزُ مِنَ الشُّرُوطِ فِي الإِسْلاَمِ وَالأَحْكَامِ وَالْمُبَايَعَةِ
Sahih al-Bukhari 2713

Narrated `Urwa:

Aisha told me, "Allah's Messenger (ﷺ) used to examine them according to this Verse: "O you who believe! When the believing women come to you, as emigrants test them . . . for Allah is Oft- Forgiving, Most Merciful." (60.10-12) Aisha said, "When any of them agreed to that condition Allah's Apostle would say to her, 'I have accepted your pledge of allegiance.' He would only say that, but, by Allah he never touched the hand of any women (i.e. never shook hands with them) while taking the pledge of allegiance and he never took their pledge of allegiance except by his words (only).

قَالَ عُرْوَةُ فَأَخْبَرَتْنِي عَائِشَةُ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ يَمْتَحِنُهُنَّ بِهَذِهِ الآيَةِ ‏{‏يَا أَيُّهَا الَّذِينَ آمَنُوا إِذَا جَاءَكُمُ الْمُؤْمِنَاتُ مُهَاجِرَاتٍ فَامْتَحِنُوهُنَّ ‏}‏ إِلَى ‏{‏غَفُورٌ رَحِيمٌ‏}‏‏.‏ قَالَ عُرْوَةُ قَالَتْ عَائِشَةُ فَمَنْ أَقَرَّ بِهَذَا الشَّرْطِ مِنْهُنَّ قَالَ لَهَا رَسُولُ اللَّهِ صلى الله عليه وسلم ‏"‏ قَدْ بَايَعْتُكِ ‏"‏‏.‏ كَلاَمًا يُكَلِّمُهَا بِهِ، وَاللَّهِ مَا مَسَّتْ يَدُهُ يَدَ امْرَأَةٍ قَطُّ فِي الْمُبَايَعَةِ، وَمَا بَايَعَهُنَّ إِلاَّ بِقَوْلِهِ‏.‏
Reference : Sahih al-Bukhari 2713
In-book reference : Book 54, Hadith 2
USC-MSA web (English) reference : Vol. 3, Book 50, Hadith 874
  (deprecated numbering scheme)