We used to take the oath of allegiance to the Prophet ﷺ to hear and obey, and he would tell: In What I am able.  

كُنَّا نُبَايِعُ النَّبِيَّ ﷺ عَلَى السَّمْعِ وَالطَّاعَةِ وَيُلَقِّنُنَا فِيمَا اسْتَطَعْتَ  

The Messenger of Allah ﷺ never touched the hand of woman, but he received the oath of allegiance from her. When he received the oath of allegiance from her, she gave it to him, and he said: Go, I have received your oath of allegiance.  

عَنْ بَيْعَةِ رَسُولِ اللَّهِ ﷺ النِّسَاءَ قَالَتْ مَا مَسَّ رَسُولُ اللَّهِ ﷺ يَدَ امْرَأَةٍ قَطُّ إِلاَّ أَنْ يَأْخُذَ عَلَيْهَا فَإِذَا أَخَذَ عَلَيْهَا فَأَعْطَتْهُ قَالَ اذْهَبِي فَقَدْ بَايَعْتُكِ  

who was a Companion, reported that his mother Zainab daughter of Humain went to the Messenger of Allah ﷺ and said: Messenger of Allah, receive the oath of allegiance from him. The Messenger of Allah ﷺ said: He is Minor. He then wiped his head.  

وَكَانَ قَدْ أَدْرَكَ النَّبِيَّ ﷺ وَذَهَبَتْ بِهِ أُمُّهُ زَيْنَبُ بِنْتُ حُمَيْدٍ إِلَى رَسُولِ اللَّهِ ﷺ فَقَالَتْ يَا رَسُولَ اللَّهِ بَايِعْهُ فَقَالَ رَسُولُ اللَّهِ ﷺ هُوَ صَغِيرٌ فَمَسَحَ رَأْسَهُ