SB 4.24.32

maitreya uvāca
ity anukrośa-hṛdayo
 bhagavān āha tāñ chivaḥ
baddhāñjalīn rāja-putrān
 nārāyaṇa-paro vacaḥ
Word for word: 
maitreyaḥ uvāca — the great saint Maitreya continued to speak; iti — thus; anukrośa-hṛdayaḥ — very kindhearted; bhagavān — the lord; āha — said; tān — unto the Pracetās; śivaḥ — Lord Śiva; baddha-añjalīn — who were standing with folded hands; rāja-putrān — the sons of the King; nārāyaṇa-paraḥ — Lord Śiva, the great devotee of Nārāyaṇa; vacaḥ — words.
Translation: 
The great sage Maitreya continued: Out of his causeless mercy, the exalted personality Lord Śiva, a great devotee of Lord Nārāyaṇa, continued to speak to the King’s sons, who were standing with folded hands.
Purport: 

Lord Śiva voluntarily came to bless the sons of the King as well as do something beneficial for them. He personally chanted the mantra so that the mantra would be more powerful, and he advised that the mantra be chanted by the King’s sons (rāja-putras). When a mantra is chanted by a great devotee, the mantra becomes more powerful. Although the Hare Kṛṣṇa mahā-mantra is powerful in itself, a disciple upon initiation receives the mantra from his spiritual master, for when the mantra is chanted by the spiritual master, it becomes more powerful. Lord Śiva advised the sons of the King to hear him attentively, for inattentive hearing is offensive.