SB 3.15.35
tesam itiritam ubhav avadharya ghoram
tam brahma-dandam anivaranam astra-pugaih
sadyo harer anucarav uru bibhyatas tat-
pada-grahav apatatam atikatarena
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
When the doormen of Vaikunthaloka, who were certainly devotees of the Lord, found that they were going to be cursed by the brahmanas, they at once became very much afraid and fell down at the feet of the brahmanas in great anxiety, for a brahmana’s curse cannot be counteracted by any kind of weapon.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Although, by chance, the doormen committed a mistake by checking the brahmanas from entering the gate of Vaikuntha, they were at once aware of the gravity of the curse. There are many kinds of offenses, but the greatest offense is to offend a devotee of the Lord. Because the doormen were also devotees of the Lord, they were able to understand their mistake and were terrified when the four Kumaras were ready to curse them.