[Rebbe Nachman] said that if you cannot converse [with God], but can just say one word, you should be strong-minded and say that one word many, many times, without end or number. Even if you spend many days repeating just that one word alone, it is also very good. You should be strong-minded and determined, and continue to say that one word over and over, countless times, until God, blessed be He, has compassion on you, and opens your mouth so that you can converse with Him freely. (Likkutei Moharan, Tinyana, #96, quoted in Hishtapchut ha-Nefesh)

He said that when you were only able, during hitbodedut, to say the phrase, "Master of the World!" [Ribono shel Olam], it is also very good. (Hayei Moharan, Part 2, p. 15, quoted in Hishtapchut ha-Nefesh)

Yitzhak Buxbaum in Jewish Spiritual Practices