This is the full text of the First Presidency Statement from 15 February 1978. I found it in Spencer Palmer's The Expanding Church. Bits and pieces are quoted all over and this book has been the only place I've seen the full text. This is the entire statement all together, quoted in its entirety.
Based upon ancient and modern revelation, The Church of Jesus Christ of Latter-day Saints gladly teaches and declares the Christian doctrine that all men and women are brothers and sisters, not only by blood relationship from common mortal progenitors, but also as literal spirit children of an Eternal Father.
The great religious leaders of the world such as Mohammed, Confucius, and the Reformers, as well as philosophers including Socrates, Plato, and others, received a portion of God's light. Moral truths were given to them by God to enlighten whole nations and to bring a higher level of understanding to individuals.
The Hebrew prophets prepared the way for the coming of Jesus Christ, the promised Messiah, who should provide salvation for all mankind who believe in the gospel.
Consistent with these truths, we believe that God has given and will give to all peoples sufficient knowledge to help them on their way to eternal salvation, either in this life or in the life to come.
We also declare that the gospel of Jesus Christ, restored to his Church in our day, provides the only way to a mortal life of happiness and a fulness of joy forever. For those who have not received this gospel, the opportunity will come to them in the life hereafter if not in this life.
Our message therefore is one of special love and concern for the eternal welfare of all men and women, regardless of religious belief, race, or nationality, knowing that we are truly brothers and sisters because we are the sons and daughters of the same Eternal Father.