"There is in the Old Testament no indication of distinctions in the Godhead; it is an anachronism to find either the doctrine of the Incarnation or that of the Trinity in its pages"
("God," Encyclopedia of Religion and Ethics, Vol. 6, p. 254).
"Theologians today are in agreement that the Hebrew Bible does not contain a doctrine of the Trinity"
(The Encyclopedia of Religion, ed. Mircea Eliade, Macmillan Publishing Company, 1987,
Vol. 15, p. 54).
"The doctrine of the Trinity is not taught in the Old Testament"
(New Catholic Encyclopedia, 1967, Vol. XIV, p. 306).
"The Old Testament tells us nothing explicitly or by necessary implication of a Triune God who is Father, Son and Holy Spirit.... There is no evidence that any sacred writer even suspected the existence of a [Trinity] within the Godhead.... Even to see in the Old Testament suggestions or foreshadowings or ‘veiled signs’ of the Trinity of persons, is to go beyond the words and intent of the sacred writers"
(Edmund J. Fortman, The Triune God, Baker Book House, 1972, pp. xv, 8, 9).
"The Old Testament is strictly monotheistic. God is a single personal being. The idea that a Trinity is to be found there is utterly without foundation."
"There is no break between the Old Testament and the New. The monotheistic tradition is continued. Jesus was a Jew, trained by Jewish parents in the Old Testament scriptures. His teaching was Jewish to the core; a new gospel indeed but not a new theology…And he accepted as his own belief the great text of Jewish monotheism:
Hear, O Israel, the Lord our God is one God"
(L.L. Paine, A Critical History of the Evolution of Trinitarianism, Houghton Mifflin and Co., 1900, p. 4).
Taken From: http://focusonthekingdom.org/articles/trinity.htm