William E. McLellin dates the Fanny Alger "Transaction" to this date in a letter to Joseph Smith III, written 70 years later about his conversation with Emma about Fanny Alger
"Your father [written to Joseph Smith III] committed an act with a Miss Hill—a hired girl. Emma saw him, and spoke to him. He desisted, but Mrs. Smith refused to be satisfied. He called in Dr. Williams, O. Cowdery, and S. Rigdon to reconcile Emma. But she told them just as the circumstances took place. He found he was caught. He confessed humbly, and begged forgiveness. Emma and all forgave him."
An author pseudo named "Historicus" also writes that it occurred on this day
She [Emma Smith] discovered that Joseph had been celesitalizing with this maiden, Fanny, who acknowledged the truth, but Joseph denied it in toto and stigmatized the statement of the girl as a base fabrication. Emma, of course, believed the girl, as she was very well aware that no confidence could be placed in her husband, and she became terrible worked up about it. She was like a mad woman, and acted so violently that Oliver Cowdery and some of the elders were called in to minister to her and 'cast the devil out of sister Emma."
[Source: Letter to Joseph Smith, III, July 1872, Community of Christ Archives, reprint in Stan Larson and Samuel J. Passey, eds., The William E. McLellin Papers, 1854-1880; in Exploring Mormonism: Polygamy Timeline, http://www.exploringmormonism.com/polygamy-timeline/]