These are attainments on the treshold of Nibbana, they are an attainment of that nibbananirodha-principle which is the immediacy by which taints are destroyed.
- Emptiness, the signless, & the undirected are names for a state of concentration that lies on the threshold of Unbinding. They differ only in how they are approached. According to the commentary, they color one's first apprehension of Unbinding: a meditator who has been focusing on the theme of inconstancy will first apprehend Unbinding as signless; one who has been focusing on the theme of stress will first apprehend it as undirected; one who has been focusing on the theme of not-self will first apprehend it as emptiness.
These nibbananirodha attainments are talked about as path-fruition attainments, or as signless[themeless]/undirected/emptiness release depending on how the are approched, depending on how they are apprehended and whether any & what change is seen in one who emerges from them.
This attainment is the difference between a dhamma-follower and a stream-enterer who has directly seen the truth of cessation.
One can become absorbed for up to 7 days & 7 nights, dwelling sensitive to unalloyed pleasure of the Asoka [sorrowless] reality.
Now, I — without moving my body, without uttering a word — can dwell sensitive to unalloyed pleasure for a day and a night... for two days & nights... for three... four... five... six... seven days & nights. - MN 14
"And what, Ananda, is another pleasure more extreme & refined than that [of neither perception nor non perception]? There is the case where a monk, with the complete transcending of the dimension of neither perception nor non-perception, enters & remains in the cessation of perception & feeling. This is another pleasure more extreme & refined than that. Now it's possible, Ananda, that some wanderers of other persuasions might say, 'Gotama the contemplative speaks of the cessation of perception & feeling and yet describes it as pleasure. What is this? How can this be?' When they say that, they are to be told, 'It's not the case, friends, that the Blessed One describes only pleasant feeling as included under pleasure. Wherever pleasure is found, in whatever terms, the Blessed One describes it as pleasure.' - SN 36.19
Here, venerable sir, whenever we want, by completely surmounting the base of neither-perception-nor-non-perception, we enter upon and abide in the cessation of perception and feeling. And our taints are destroyed by our seeing with wisdom. - MN 31
There are, monks, three unskilled ways of thought: thoughts of lust, thoughts of ill-will, thoughts of hurting. And these three unskilled states disappear utterly in him whose heart is well established in the four foundations of mindfulness, or who practices concentration on the signless. - SN 22.80
Practicing signless release utterly destroys taints and that result [arahantship] is called 'the unprovoked release'.
"Passion is a making of themes, aversion a making of themes, delusion a making of themes. For a monk whose fermentations are ended these have been abandoned, their root destroyed, made like a palmyra stump, deprived of the conditions of development, not destined for future arising. To the extent that there are themeless awareness-releases, the unprovoked awareness-release is declared supreme. And that unprovoked awareness-release is empty of passion, empty of aversion, empty of delusion. - SN 41.7
Here some favorite texts from Therigatha
Four times, five, I ran amok from my dwelling,
having gained no peace of awareness,
my thoughts out of control.
So I went to a trustworthy nun.
She taught me the Dhamma:
aggregates, sense spheres, & elements.
Hearing the Dhamma,
I did as she said.
For seven days I sat in one spot,
absorbed in rapture & bliss.
On the eighth, I stretched out my legs,
having burst the mass
of darkness. -Thig 3.2
[I thought:] "Plowing the field with plows, sowing the ground with
seed, supporting their wives & children, young men gather up wealth.
So why is it that I, consummate in virtue, a doer of the teacher's
bidding, don't gain Unbinding? I'm not lazy or proud."
Washing my feet, I noticed the water.
And in watching it flow from high to low, my heart was composed
like a fine thoroughbred steed.
Then taking a lamp, I entered the hut, checked the bedding, sat down
on the bed. And taking a pin, I pulled out the wick: Like the flame's
unbinding was the liberation of awareness. - Thig 5.10
This last line of verse is noteworthy to dhamma-nerds because liberation of awareness also occurs as 'awareness freed from consciousness' in Bahuna sutta.
Freed, dissociated, & released from ten things, Bahuna, the Tathagata dwells with limitless awareness. Which ten? Freed, dissociated, & released from form, the Tathagata dwells with limitless awareness. Freed, dissociated, & released from feeling... Freed, dissociated, & released from perception... Freed, dissociated, & released from fabrications... Freed, dissociated, & released from consciousness... Freed, dissociated, & released from birth... Freed, dissociated, & released from aging... Freed, dissociated, & released from death... Freed, dissociated, & released from stress... Freed, dissociated, & released from defilement, the Tathagata dwells with limitless awareness - AN 10.81