The Supreme Personality of God (Krsna) said: The great saint Narada Muni is very merciful. By his curse, he showed the greatest favor to both of you (Nalakuvara & Manigriva), who were mad after material opulence & who had thus become blind - SB 10.10.40

Expressions researched:
"The Supreme Personality of Godhead said: The great saint Nārada Muni is very merciful. By his curse, he showed the greatest favor to both of you, who were mad after material opulence and who had thus become blind"

Srimad-Bhagavatam

SB Canto 10.1 to 10.13

The Supreme Personality of Godhead said: The great saint Nārada Muni is very merciful. By his curse, he showed the greatest favor to both of you, who were mad after material opulence and who had thus become blind.

SB 10.10.40, Translation and Purport

The Supreme Personality of Godhead said: The great saint Nārada Muni is very merciful. By his curse, he showed the greatest favor to both of you, who were mad after material opulence and who had thus become blind. Although you fell from the higher planet Svargaloka and became trees, you were most favored by him. I knew of all these incidents from the very beginning.

It is now confirmed by the Supreme Personality of Godhead that the curse of a devotee is also to be regarded as mercy. As Kṛṣṇa, God, is all-good, a Vaiṣṇava is also all-good. Whatever he does is good for everyone. This is explained in the following verse.