The Prophet ﷺ used to eat watermelon with fresh dates.
حدثنا عبدة بن عبد الله الخزاعي حدثنا معاوية بن هشام عن سفيان عن هشام بن عروة عن أبيه
أن النبي ﷺ كان يأكل البطيخ بالرطب
No references are available.
[Sahih] Abu Dawud also narrated it, Foods, Chapter on Combining Two Types (of Food), no. 3836, and others through various routes from Hisham, from him. See Musnad Humaydi, no. 256 (my edition). There is also a report on this subject from Anas in Hakim, 4/120, 121.