S. R. Faruqi:

In Persian they use for henna the simile of a bird, because for color vanishing or becoming light they use 'for the color to fly' [rang uṛnā]. They also use for the heart the simile of a bird. In the present verse the nah is for admonition and emphasis [tākīd]. The idea is that the way the bird of the color of henna, having flown from the beloved's hand, doesn't come back, in the same way my heart, when it was released from her hand, went away forever and ever.

The 'went' is full of meaning-- that is, it was destroyed, it died, it vanished, all sign or trace of it was lost; all these meanings are present. As long as the heart remained in the beloved's hand, that was fine. When once it was released [chhūṭ gayā], then there was no trace of it-- of where it was destroyed, of where it died. The prose of the second line will be: dil us ke hāth se chhūṭāa nah [aur] gayā . Since there's blood in the heart, to call it the bird of the color of henna is also pleasurable.

[See also {115,1}.]

FWP:

SETS
MOTIFS
NAMES
TERMS == SIMILE

The color of henna lasts for some days, then begins to fade away gradually. (For a discussion of henna, with illustrations, see G{18,4}.) What would it mean for that color to be imagined as a 'bird'? Presumably, it would be a bird that when released, would remain for some time, and then gradually fade away. In other words, it would be a bird that would 'fly' only in the sense of fading away or dying. In somewhat the same way, when the heart was released from the beloved's hand, it did not fly off anywhere, but gradually faded away and died.

One enjoyable use for nah is this colloquial one, parallel to the identifying, attention-focusing use of 'you know?' in English ('Just hand me that folder-- you know?-- the one in the top drawer'). Here, such a nah might suggest that the heart is so long gone that the addressee would hardly recall it, and would need to have a bit of a nudge to his or her memory. Or perhaps since SRF considers the nah to be admonitory or emphatic, it demands assent ('Sinners like him-- isn't it so?-- are bound to come to a bad end'). I used to know someone who said hai , nah ? at the end of almost every sentence. (Think of the Indian English 'isn't it?'.) Other such colloquial nah examples: {52,3} (in which SRF describes it as 'emphatic'); {847,9}; {851,1}.

Several members of our poetry group favored (Mar. 2016) a reading that took the nah seriously as negating the whole two-line utterance: 'The heart did not, like the bird of the color of henna, become released and go'. That is, the henna-color bird left the beloved's hand, but the heart did not do so; either it was not released at all, or when it was released it did not go.

Along similar lines, Mir Kazim Ali has proposed (Apr. 2020) that the nah applies only to the second line: like the henna-color bird, the heart stayed around for a while and did not go at once, but faded away gradually (since the process of rang uṛnā is a prolonged one).

Both these readings have to recognize, though, that the nah is extraordinarily far away from the chhūṭā , and even farther from the gayā . So no matter which reading we choose, the nah remains a somewhat awkward presence in the second line.

On the grammar of chhūṭā gayā , see {52,1}.