ANSWER:

Omer may Allah be pleased with him could have sought the waseelah from our prophet salla Allahu alaihi wa sallam if this was permissible as he is way better than Al Abbas, though he did not!

This tells you that he wasn’t asking waseelh through Al Abbas, may Allah be pleased with him, rather he was asking him to make duaa to Allah due to his relationship to the prophet salla Allahu alaihi wa sallam. 

He stood up and asked Allah for rain.

This is why whoever seeks the waseelah from deceased people, this is shirk.

QUESTION: Sahih al-Bukhari 1010 mentions that Umar (RA) sought rain through Al-Abbas (RA). Does this hadith prove tawassul is permissible in Islam? Is this considered bid‘ah or a valid practice according to scholars?