Parley P. Pratt explains how he introduced Sidney Rigdon to the Book of Mormon.
Parley P. Pratt, Mormonism Unveiled (Painesville, Ohio: Wm. D. Pratt, 1838), 38-40
About A.D. 1827, Messrs. A. Campbell, W. Scott, and S. Rigdon, with some others, residing in Virginia, Ohio, &tc. came off from the Baptist, and established a new order, under the name of Reformed Baptists, or Disciples; and they were termed by their enemies, Campbellites, Rigdonites, &c. This reformation, as to its Doctrine, consisted principally, of the Baptism of Repentance, for Remission of Sins, &c. And Mr. Rigdon, in particular, held to a literal fulfilment and application of the written word; and by this means he was an instrument to turn many from the false notions of Sectarian Traditions, to an understanding of the Prophecies, touching the great restoration of Israel, and the mighty revolutions of the last days. Many hundred disciples were gathered by his ministry throughout the Lake Country of Ohio; and many other preachers stood in connection with him in those principles. I was then pursuing an agricultural life, and mostly occupied in converting the wilderness into a fruitful field; but being a member of the Baptist Church, and a lover of truth, I became acquainted with Mr. Rigdon, and a believer in, and a teacher of the same doctrine. After proclaiming those principles in my own neighborhood and the adjoining country, I at length took a journey to the State of New-York, partly on a visit to Columbia County, N.Y., my native place; and partly for the purpose of ministering the word. This journey was undertaken in August, 1830. I had no sooner reached Ontario Co. N.Y., than I came in contact with the "Book of Mormon," which had then been published about six months, and had gathered about fifty disciples, which were all that then constituted the Church of the Latter Day Saints. I was greatly prejudiced against the Book; but remembering the caution of Paul, "Prove all things and hold fast that which is good," I sat down to read it; and after carefully comparing it with the other Scriptures, and praying to God, He gave me the knowledge of its truth, by the power of the Holy Ghost; and what was I, that I should withstand God? I accordingly obeyed the Ordinaces, and was commissioned by Revelation; and the laying on of hands to preach the fulness of the Gospel, Then, after finishing my visit to Columbia Co., I returned to the brethren in Ontario Co., where for the first time, I saw Mr. Joseph Smith, Jr., who had just returned from Pennsylvania, to his father's house, in Manchester. About the 15th of October, 1830, I took my journey, in company with Elder O. Cowdery, and Peter Whitmer, to Ohio. We called on Elder S. Rigdon, and then for the first time, his eyes beheld the "Book of Mormon;" I myself, had the happiness to present it to him in person. He was much surprised, and it was with much persuasion and argument, that he was prevailed on to read it, and after he had read it, he had a great struggle of mind, before he fully believed and embraced it; and when finally convinced of its truth, he called together a large congregation of his friends, neighbors, and brethren, and then addressed them very affectionately, for near two hours, during which time, both himself and nearly all the congregation were melted into tears. He asked forgiveness of every body who might have had occasion to be offended with any part of his former life; he forgave all who had persecuted or injured him, in any manner; and the next morning, himself and wife, were baptised by elder O. Cowdery. I was present, it was a solemn scene, most of the people were greatly affected: they came out of the water overwhelmed in tears. Many others were baptised by us in that vicinity, both before and after his baptism—insomuch, that during the fall of 1830, and the following winter and spring, the number of disciples were increased to about 1000; the Holy Ghost was mightily poured out, and the word of God grew and multiplied; and many priests obedient to the Faith. Early in 1831, Mr. Rigdon having been ordained under our hands, visited elder J. Smith, Jr. in the state of New York, for the first time; and from that time forth, rumor began to circulate, that he (Rigdon) was the author of the Book of Mormon. The Spaulding story never was dreamed of until several years afterwards, when it appeared in "Mormonism Unveiled," a base forgery, by D. P. Hulburt, and others of similar character, who had long strove to account for the Book of Mormon, in some other way besides the truth. In the west, whole neighborhoods embraced Mormonism, after this fable of the Spaulding story, had been circulated among them; indeed, we never conceived it worthy of an answer, until it was converted by the ignorant and impudent dupes or knaves, in this city, who stand at the head of certain religious papers, into something said to be positive, certain, and not to be disputed! Now I testify, that the forgers of the Spaulding lie, (concerning S. Rigdon and others,) are of the same description as those who forged the lie against the disciples of old—accusing them of stealing the body of Jesus, &c. And those who love this lie, are no better. I mean the editors of the N. Y. Evangelist, Zion's Watchman, and all others who are equally guilty, including all who read and believe such a thing. And except they repent they will have their part with drunkards, whoremongers, sorcerers, thieves, murderers, etc., for being guilty of loving or making a lie; and in that day when the secrets of all hearts shall be made manifest: then shall they know, that these things and many others were base falsehoods, put in circulation by the devil and his servants; and that the Book of Mormon, is a record of eternal truth, which speaks from the dust, as a voice from the dead, bearing record of the Gospel of a crucified and risen Redeemer, reproving the sins of the world, and warning them of the things which must shortly come to pass; therefore, repent, all ye ends of the earth, and be baptised for remission of sins, and you shall receive the gift of the Holy Ghost; and signs shall follow those that believe; and this Gospel of the kingdom shall first be preached among all Nations, and then shall the Son of Man come. Amen.