“I just depend on a lot of prayer and meditation. I believe that without God I am nobody, but that with God, I can do anything.”

Johannesburg, South Africa, 2 May, 1972
1970s

Source: Echoes from the Bottomless Well (1985), p. 65

Controversy
Song lyrics, Controversy (1981)

Statement published in A Year of Beautiful Thoughts‎ (1902) by Jeanie Ashley Bates Greenough, p. 172, Third statement for June 11. This has often been misattributed to Helen Keller in some published works since at least 1980, perhaps because she somewhere quoted it.
Variant:
I am only one,
But still I am one.
I cannot do everything,
But still I can do something;
And because I cannot do everything,
I will not refuse to do the something that I can do.
The Book of Good Cheer : A Little Bundle of Cheery Thoughts‎ (1909) by Edwin Osgood Grover, p. 28; also in Masterpieces of Religious Verse (1948) by James Dalton Morrison, p. 416, where it is titled "Lend a Hand"

Letter to Yale University (1899), quoted in Henry F. Pringle, William Howard Taft: The Life and Times, vol. 1, p. 45 (1939).

As quoted in Life on the Circuit with Lincoln (1892) by Henry Clay Witney
Posthumous attributions

2000s, The Sacred Warrior (2000)
Context: His philosophy of Satyagraha is both a personal and a social struggle to realize the Truth, which he identifies as God, the Absolute Morality. He seeks this Truth, not in isolation, self-centeredly, but with the people. He said, "I want to find God, and because I want to find God, I have to find God along with other people. I don't believe I can find God alone. If I did, I would be running to the Himalayas to find God in some cave there. But since I believe that nobody can find God alone, I have to work with people. I have to take them with me. Alone I can't come to Him."

Source: The Diary of an Old Soul & the White Page Poems