The believer is happy, the doubter is wise. - Irish Proverb
If you are going to be a doubter, I don't need your negative energy. - Stephen Richards
The vain man is generally a doubter. It is Newton who sees himself as child on the sea shore, and his discoveries in the colored shell.
I am an infidel today. I do not believe what has been served to me to believe. I am a doubter, a questioner, a skeptic. When it can be proved to me that there is immortality, that there is resurrection beyond the gates of death, then will I believe. Until then, no. - Luther Burbank