Boron internal ADC max impedance

Hi there,
I have a Boron and I would like to measure a signal around 5V with one of the analogue pins using a voltage divider.
To prevent the voltage divider from loading the input and distorting the signal, I want to use the highest value resistors I can possibly get away with - hence my question.
What is the maximum input impedance that the analogue pins can cope with while still giving an accurate reading? I couldn’t find it in the online datasheet unfortunately.
Would a 9.1M and a 4.7M resistor allow enough current though?

On the Nordic forum there was a similar question

Particularly this table and schema may be of interest for your question

Your signal source needs to allow for the 2.5pF sampling cap to fully charge in time.