The third Karmapa, Rangjung Dorje, composed two short texts, Shastra Presenting the Heart Essence and Shastra Distinguishing Consciousness and Wisdom. སྙིང་པོ་བསྟན་པའི་བསྟན་བཅོས། རྣམ་ཤེས་ཡེ་ཤེས་འབྱེད་པའི་བསྟན་བཅོས།
His intention was that students, who understood Maitreya's Buddha Nature through these two texts would comprehend mahāmudrā meditation.
For now, you find teachings from Karma Chodrub Gyamtso Ling, Brussels 1997.
Tibetan - English - French
4 talks, audio