Question Summary:
What is the ruling of eating food at bidah gatherings?

Question Detail:

What is the rluing on eating the foods that distributed on mawlids and bidah occasions, will we be sinful for partaking?

Answer :

In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
 
It is prohibited to attend gatherings in which the laws of Shariah are violated. Hence, eating and drinking at such gatherings will also be impermissible.[1]
And Allah Ta’āla Knows Best
Muhammad Haris Siddiqui
Student Darul Iftaa
Melbourne, Australia 
Checked and Approved by,
Mufti Ebrahim Desai.