Did you not read the article?
It is a sweet and pious belief that the infusion of Mary's soul was effected without original sin; so that in the very infusion of her soul she was also purified from original sin and adorned with God's gifts, receiving a pure soul infused by God; thus from the first moment she began to live she was free from all sin" (Sermon: "On the Day of the Conception of the Mother of God," 1527)
However, I'd suggest a little further research on Luther's views:
The next tidbit offered by Marshall is the following Luther quote:
The sermon was taken down in notes and published with Luthers approval. The same statements concerning the Immaculate Conception still remain in a printed edition published in 1529, but in later editions which appeared during Luthers lifetime they disappear.
The reason for their disappearance is that as Luthers Christocentric theology developed, aspects of Luthers Mariology were abandoned. Grisar also recognizes the development in Luther's theology. In regards to the Luther quote in question, Grisar says (from a Roman Catholic perspective):
As Luthers intellectual and ethical development progressed we cannot naturally expect the sublime picture of the pure Mother of God, the type of virginity, of the spirit of sacrifice and of sanctity to furnish any great attraction for him, and as a matter of fact such statements as the above are no longer met with in his later works.
Did Martin Luther believe in the Immaculate Conception of Mary?