SB 7.5.21
aropyankam avaghraya
murdhany asru-kalambubhih
asiñcan vikasad-vaktram
idam aha yudhisthira
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Narada Muni continued: My dear King Yudhisthira, Hiranyakasipu seated Prahlada Maharaja on his lap and began smelling his head. With affectionate tears gliding down from his eyes and moistening the child’s smiling face, he spoke to his son as follows.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
If a child or disciple falls at the feet of the father or spiritual master, the superior responds by smelling the head of the subordinate.