This would seem to surpass mere rumour.
Corroborated Evidence from various sources.
Seems I missed a good Documentary!...:(
I know! Who could believe it?!
I didn't believe it when I watched the documentary about Lincoln on the History Channel so I researched it too.
The second source for the story that Lincoln slept with Derickson is Thomas Chamberlin, an officer of the regiment that guarded Lincoln. Chamberlin wrote in his 1895 book.
There is what might be called circumstantial evidence: that as a young man Lincoln allegedly lacked interest in eligible women, or that he allegedly began puberty at an unusually early age, which Tripp argues is correlated to homosexuality in adult men. On its own, this circumstantial evidence could never convince a skeptic, though it can perhaps add depth and texture to the discussion of the second category of evidence, which might be called the direct evidence: that Lincoln is known to have slept in the same bed with a number men, including the closest friend of his young adulthood, Joshua Speed. Lincoln's relationships with Speed and other men in Illinois with whom he shared a bed have long been known and incorporated into the literature. The episode of bed-sharing that has recently caught the public eye, however, and that even has given pause to esteemed Lincolnists like David Donald, is the scene depicted in two sources that Lincoln, while president, slept with one of his bodyguards when Mary Lincoln was not at home.