Among the many oral instructions the first Karmapa  received from Gampopa was the mahamudra view that thoughts need not be artificially amputated during meditation. Gampopa said, "This co-emergent unification of ours is one of our key oral instructions. Whatever thought occurs in your conscious mind, no matter how much you may want it or not want it, you simply observe that thought as mind. Likewise, whatever arises as appearances is seen as mind. In this way, we take thoughts and appearances onto the path. Thoughts are not the problem; it is our discursive attachment to those thoughts that creates obstacles." 
[1. Düsum Khyenpa (1110-1193).]
[2. Dudjom Lingpa (1835-1904) takes the same approach in his dzogchen (primordial state) instructions. He calls it, "taking the impure mind as the path".]
After Karmapa had practiced in retreat for a time, he felt he had a genuine experience of bliss, luminosity, and non-conceptuality, so, he told Gampopa about it. The teacher replied, "Ah, you looked directly at it; that’s good. Now tell me—where did the root of those experiences come from?" Dusum Khyenpa couldn’t answer that, so Gampopa said, "Well then, you need to continue to meditate just like that. Meditate often, but only for short sessions. Keep that up, and whatever else you do, make consciousness your servant!"
So Karmapa continued alternating like this, meditating in retreat and then discussing it with Gampopa. One night he dreamt that a monk appeared and explained a new dharma to him that he had not heard before. The dream was very lucid, so he hurriedly reported it to his guru. Gampopa asked him, "Did you like that dream?" Karmapa said yes indeed, he liked it a lot! Gampopa flew into a rage and rebuked his student, "Listen, you are going to have all sorts of marvels happening when you meditate, but you have to understand that they are all just illusory appearances. Treat them as illusory appearances, and they will turn into the path. But, if you hold those appearances to be real entities, they will remain obstacles! So, whatever comes up in mind, do not cling to any of it as good, and do not reject any of it as bad. Understand all of it to be non-dual. Whenever a thought arises, don’t let it spawn a discursive stream of analysis; know it simply as conditioned mind arising from latent karma, and let it go."
So, Karmapa continued this sequence of retreats and interviews, and one day he came down and reported, "The rigpa  that I have developed is usually clear during the day, but at night there is still distraction."
[3. Knowledge of the primordial state. en.wikipedia.org/wiki/Rigpa ]
Gampopa answered, "Yes, you still have a fault. You have the fault that when the awareness is clear you like it, and when it is not clear, you don't! That is not the right approach. Put your rigpa in empty clarity as usual, and then whatever arises, know it as non-dual mind. During the day, the luminosity will mix rigpa with appearances, and at night the luminosity will mix with dreams. No matter what arises, remain in equanimity. When you are among crowds, regulate your speech and meditate! Whatever you are doing, be mindful of the stillness of your awareness in the midst of the movements of samsara."
So, Karmapa continued on with his practice, and eventually he was able to report progress to Gampopa. He said, "Finally, my abiding has lessened. When I entrusted everything to pure rigpa, any discursive thought that arose also went into the state of pure rigpa. As each discursive thought arose, the experience was deepened by it. Then, when I let that rigpa go free as well, an experience of luminous emptiness remained in unfabricated equanimity. Even in post-meditation, the result was that nothing arising in the six sense consciousnesses was reified as inherently existing externally. Everything was present as mind."
When Gampopa heard this, he replied, "Well... that’s it!"
~ Ŧoƞpa Ɉoƞ
- Adapted from the Complete Works of Gampopa, translated by Tony Duff in Gampopa Teaches Essence Mahamudra, 2011