First Tweet containing a hashtag
Surface is the first tweet in the hashtag, to know the founder of the hashtag, it is his right; and also there are those who use the hashtag for no purpose intended for topic of the hashtag (no objection to it), but you are tired to reach the news for which the hashtag was founded due to the large number of tweets outside the same topic.
This is already possible with the Search API (full archive). You can use the counts endpoint for example to find out when a hashtag was mentioned for the first time on Twitter.
Can you confirm that you're asking for a way to fetch the first Tweet that contained a given hashtag?
Saleh Alaamri commented
تثبيت اول تغريدة في الهاشتاق لمعرفة مؤسس الهاشتاق فهذا حق له ؛ وايضا لتسهيل الوصول إلى الغرض المقصود من الهاشتاق لانه يوجد الكثير من المغردين خارج السرب أو يغردون بغرض الدعاية أو الدعابة