Is this authentic?
Sunnah practices for watermelon:
The messenger of Allah (sallallahu ‘alayhi wa sallam) was gifted a watermelon. He took it sniffed it and said “Allow it to become large.”
This narration has been declared a fabrication by the Muhaddithun.
(Tanzihush Shari’ah, vol. 2 pg. 260. See the next part of the Hadith here)
It is therefore not suitable to quote and should not be regarded as a Sunnah specifically for watermelons.
However, when Nabi (sallallahu ‘alayhi wa sallam) was presented with the first [of any] fruit of the season, he would kiss it, touch it to his eyes and recite a du’a. See here.
The first watermelon of the season would therefore fall under this general Sunnah.
And Allah Ta’ala Knows best.
Answered by: Moulana Suhail Motala
Approved by: Moulana Muhammad Abasoomar
This answer was collected from HadithAnswers.com. The answers were either answered or checked by Moulana Haroon Abasoomar (rahimahullah) who was a Shaykhul Hadith in South Africa, or by his son, Moulana Muhammad Abasoomer (hafizahullah), who is a Hadith specialist.