When missionaries came to githunguri they settled I believe in a place called riruta I may be wrong. Let me take you to about 1981 I am a kid and one evening as we are in the kitchen just after dinner listening to my mum stories she started to sing this song. Ndahungukite ngiuma kwa waing'a. Njisu akihumba nguo ya uhonokio kwa
Waing'a ndigachoka. As as a kid I assumed she had made it up and sung it. Over the years I was to hear the same song over and over.
Loose transaction of the song is
I was ashy as I came from Waing'as place. Jesus took me and covered me in salvation. I will never go back to waing'as place.
Kikuyus preserved our history thru songs. The history behind this song is that..there was a measles outbreak in githunguri. Only one medicine man had a remedy for it. His name was waing'a. He had this ash that when applied it would stop the itching from blisters so anyone especially children who caught measles were taken to him and he treated them. When they left his homestead they would be covered in ash. Then a local missionary doctor came into town and started treating people and his medicine was working very well against measles and so the kikuyus recorded a song in praise of his medicine and so everyone abandoned waing'as medicine for the mzungu one. However over years waing'a has been demonized and his name has Ben synonymous to the devil.
With modern medicine the missionaries were able to recruit more covers. As kikuyus wanted to learn more about this new medicine. So kikkuyus abandoned their medicine men and religion converting into Christianity in droves.
Anyway I found this tib bit on Twitter