"[Tsongkhapa] (...) refers to the first meeting between Milarepa and Gampopa, in which Milarepa asked about Gampopa's meditation. Gampopa replied that he could sit in meditative absorption for many days at a time without distraction. Milarepa told him, "You cannot get oil by crushing sand. The practice of samadhi is not sufficient in and of itself. You should learn my system of inner heat yoga...." The implication is that the innate ecstasy conjoined with wisdom awareness, which is aroused by the inner heat yoga, was absent, and thus Gampopa's samadhi lacked real tantric power. Arousing that "real tantric power" is the purpose and territory of the inner heat doctrine. (...)"

"The Six Yogas of Naropa"

-Tsongkhapa's Commentary

Edited by Lama Glenn Mullin