One of the manifestations of the deep devotion the Companions radhiyallahu
anhum had for the Prophet sallallahu alayhi wasallam was that when a child was born in their family, they brought it to him so that he might bless it, and apply on its palate, the pulp of date etc., he had chewed himself and drop the saliva in its mouth, which they believed would have the effect of averting evil from the child and bringing it good fortune. It is called Ta'hneek in the Islaamic parlance.
Aa'ishah radhiyallahu anhaa narrates:
"People used to bring their (new-born) children to the Apostle of Allah sallallahu alayhi wasallam , and he would bless them and perform Ta'hneek."
Asmaa Binte Aboo Bakrradhiyallahu anhumaa relates that she was in the family way at the time of migration. When she migrated and came to Madeenah Munawwarah, Abdullah Ibne Zubayr radhiyallahu anhu was born to her. She relates that, "I took the child to the Apostle of Allah sallallahu alayhi wasallam and placed it on his lap. The Prophet sallallahu alayhi wasallam asked for a date, (and when it was brought), he chewed it and dropped the saliva in its mouth, and then applied the chewed date on its palate, and after it, he blessed the child. It was the first child to be born in Islaam (in the home of an emigrant, after the migration )."
instances of Ta'hneek are found in the standard
collections of the Traditions. From these, we learn that when
a child is born in a Muslim home, it should be
taken to a virtuous bondsman of Allah to receive his blessings and have
the Ta'hneek done. It is one of the Sunnah which has now sadly become extinct.