Tahneek should be performed on the day of birth.

Prophet Mohammed (pbuh) was 1,400 years ahead of Science !
Be proud to be believer of Prophet Mohammed (PBUH)

Over 1400 years ago, when a child was born, the Prophet (PBUH) made it his sunnah to take a small part of a date and place it in his mouth. He would then chew it until it was soft and then rub it onto the palate of the new born baby. This is called Tahneek.

BBC News has reported that "experts" have said - "A dose of sugar given as a gel rubbed into the inside of the cheek is a cheap and effective way to protect premature babies against brain damage"

This is why Muslims follow the sunnah of the messenger without questioning it. Science is only now discovering a tradition that was introduced 1400 years ago because Islam was and still is the forefront of development.

Link to the article - http://www.bbc.com/news/health-24224206

Hadeeth:

A'isha, the wife of the Apostle (may peace be upon him) said: babies were brought to the Messenger of Allah (may peace be upon him) and he blessed them, and after having chewed (something, e. g. dates or any other sweet thing) he rubbed there with their soft palates.
(Sahih Muslim, Book#002, Hadith #0560)
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Tahneek should be performed on the day of birth. The first preference to be used for Tahneek is normal dates, then Rutab (fresh dates), then honey and then anything sweet. The method of Tahneek is to chew the date into a paste-like substance and then to apply a small amount of that paste onto the baby's palate.
(Fathul Bari vol. 15 pg. 390)

فتح الباري لابن حجر - (ج 15 / ص 390)

قَوْله ( وَتَحْنِيكه )
أَيْ غَدَاة يُولَد ، وَكَأَنَّهُ قَيَّدَ بِالْغَدَاةِ اِتِّبَاعًا لِلَفْظِ الْخَبَر . وَالْغَدَاة تُطْلَق وَيُرَاد بِهَا مُطْلَق الْوَقْت وَهُوَ الْمُرَاد هُنَا ، وَإِنَّمَا اِتَّفَقَ تَأْخِير ذَلِكَ لِضَرُورَةِ الْوَاقِع ، فَلَوْ اِتَّفَقَ أَنَّهَا تَلِد نِصْف النَّهَار مَثَلًا فَوَقْت التَّحْنِيك وَالتَّسْمِيَة بَعْد الْغَدَاة قَطْعًا . وَالتَّحْنِيك مَضْغ الشَّيْء وَوَضْعه فِي فَم الصَّبِيّ وَدَلْك حَنَكه بِهِ ، يُصْنَع ذَلِكَ بِالصَّبِيِّ لِيَتَمَرَّنَّ عَلَى الْأَكْل وَيَقْوَى عَلَيْهِ . وَيَنْبَغِي عِنْد التَّحْنِيك أَنْ يُفْتَح فَاهُ حَتَّى يَنْزِل جَوْفه ، وَأَوْلَاهُ التَّمْرُ فَإِنْ لَمْ يَتَيَسَّر تَمْر فَرُطَب ، وَإِلَّا فَشَيْء حُلْو ، وَعَسَل النَّحْل أَوْلَى مِنْ غَيْره ، ثُمَّ مَا لَمْ تَمَسّهُ نَار كَمَا فِي نَظِيره مِمَّا يُفْطِر الصَّائِم عَلَيْهِ

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Thanks to sisters Derya Kucukali and Jaweria Hameed for introducing this news to us.