I admired George Muller's works in caring for orphans and his faith in God to provide for his need. However, I find it troubling that he didn't accept illegitimate orphans.
George Muller was a Prussian who came to Britain in 1829 in order to train for Christian missionary service. Some years later, inspired by the example of August Francke's orphanage in Halle (founded in 1696), George Muller began a similar work in Bristol. Muller's Homes - a complex of five gigantic barracks at Ashley Down, Bristol - provided accommodation for over sixteen hundred orphans mainly aged from seven to twelve years, who received an elementary education and were trained for trade or domestic service. The outstanding characteristic of Muller's work was that it depended entirely on faith in God: George Muller had no personal resources, yet he never asked for money; his Institution never went into debt; all his assistants were committed Christian believers and, on leaving, children were apprenticed to Christian employers or placed in service in Christian homes. His orphanages never attempted to be children's hospitals or reformatories; incorrigible delinquents were reluctantly expelled, and, curiously enough, George Muller did not accept illegitimate children. But the scale of Muller's work created a public awareness of the problem of orphan children, and aroused Christians to their responsibilities. George Muller was one of the early founders of the (open) Christian Brethren.
link Emphasis mine
What is his Biblical reason for not accepting illegitimate children?
While searching, I found this article and learned that it was not easy to adopt illegitimate child during their times:
I know it’s hard to believe, but foundlings [illegitimate children] generally died in the streets because there was no home for them, and adoption, as it is known today in the western world, has generally been illegal throughout most of history.
British almshouses (poorhouses) were more difficult to get into than either of the other institutions [Charles Spurgeon's and Muller's orphanages] mentioned in the first paragraph. Spurgeon and Muller both lamented the cruel system of gathering signatures, securing votes, and the complex paper work necessary to place a child into an almshouse. Most almshouses were notoriously horrible places. 90% of the foundlings who went into almshouses died before reaching 10 years old. It took Thomas Coram, a wealthy retired shipbuilder who was shocked to see dead babies in the streets of London, years to get legal permission to open the first home for foundlings. Afterwords his legal charter was repeatedly debated, and at one point rescinded, because saving foundlings was considered a corrupting influence on society.
Could it be that George Muller tried to avoid running afoul with the law or is it that, sadly, he shared with the his society the social stigma on illegitimate children?