I never obtained any confirmation about the authenticity of the following prediction, supposingly written by Trungpa Rinpoche. Please leave a comment if you have further informations about the question whether or not it was authentic.
From Shamar Rinpoches website:
While living at Rumtek monastery in Sikkim, Shamar Rinpoche received this prediction letter from Chogyam Trungpa Rinpoche in the late 1970’s.
Before writing this prediction, Trungpa Rinpoche did the practice of prasena for Dorje Yudronma, a female deity. He invoked Yudronma and asked her to give a prediction concerning the future life of Shamar Rinpoche. Then, following tradition, the text of the prediction appeared in a mirror. Trungpa Rinpoche copied the words in his own hand, composing the letter below.
Prediction about the life of Kyabje Shamar Rinpoche
The Vajra-Spring is permanent and unchanging.
Unobstructed Yudronma revealed through the list of verses profound, clear symbolic words.
The devi of long life who shines like an emerald,
Always keep at the center of your heart.
Youth is the messenger of the god of desire who will be burned by the fire of samadhi.
You should do the practice on the wrathful aspect of Guru Rinpoche (Padmasambhava).
You, the Ruby-crowned one, may burn away the darkness of the era.
In your 50th year,
Do the practice of the essence of the Buddha of Long Life and
The practice of Vajrakilaya to counter black magic.
Wash yourself with the water of Mamaki deities.
An elephant who has been intoxicated by poison will slander and create fighting within the lineage.
So take extreme caution against the corruption and trembling within the lineage.
The wealthy yellow dialecticians will harm the genuine lineage of the Kagyu dharma,
So you should strive to sharpen the spear-tip of your mind.
The Vajra-rock which is golden and shining is where you should abide in holy meditation.
You should do the three year, three month retreat.
Through the white luminosity of Vajrasattva you will go to the place of the Dharmakaya which is beyond meditation.
Keep that meaning in your heart.
 An aspect of Tara
 literally ‘Goddess’ – refers to Yudronma
 literally “burned by the fire at the end of the kalpa”. The oral explanation given by Shamar Rinpoche is that this is a warning to not follow the temptations of youthful desire, to avoid the trap of worldly life by means of the remedy of samadhi.
 Shamar Rinpoche: Sha=hat; mar=red
 literally “10 X 50 rounds”
 literally “…within.”
 According to the tradition of both the Kagyu and Nyingma schools, this term usually refers to the government of the Dalai Lama.