Sahih Bukhari: Hadith 2610

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).