Scotland's People lists a baptism of Peter, son of Alexander Cumming and Margaret Stuart, in Inveravon on 27 May 1821.
He is probably the 20-year-old mason, born Banffshire, in the household of William Richardson, gardener, at Buchromb House in the parish of Mortlach in the 1841 census.
His baptism is indexed in the IGI as Peter Cumming or Stuart, which suggests that he was illegitimate.
There is a minute in the Inveravon Kirk Session records: 27th May 1821 .... Compeared Alexr Cumming in Knocknashalg and acknowledg'd himself Father of a child, which had been born in fornication by Margaret Stuart, his servant, and begged that he might be allowed to satisfy the discipline of the Church. He was accordingly exhorted to repentance, rebuked, fined, and dismissed.
Interestingly, there is no mention of Margaret Stuart being summoned to answer for her sin. I speculate, therefore, that she was probably a Roman Catholic, Inveravon being one of the areas where there was a significant RC population while most of the country was staunchly Presbyterian.