Looking on the internet deeply has found these results:

one should help his friend for difficulty is the most popular phrase on the web.

one should help his friend in difficulty 110 results on the web	one should help his friend for difficulty 1154,000,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
It doesn't look like this phrase is very popular! The search could not find any examples on the internet.	But Charlie drowned trying to help his friends find rescue. And we know he chose to help his friends hold people up at gunpoint. He betrayed his friends for money. That should help his foot grow back. He told me himself... that he wanted to help his friend that drowned in the pool. If Childs is threatening you, Peter wants to help his friends in any way he can. Fix his BP, that should help his mental status. A man should help his friends.

one should help his friend in difficulty

110 results on the web

one should help his friend for difficulty

1154,000,000 results on the web

More popular!

It doesn't look like this phrase is very popular! The search could not find any examples on the internet.

But Charlie drowned trying to help his friends find rescue.
And we know he chose to help his friends hold people up at gunpoint.
He betrayed his friends for money.
That should help his foot grow back.
He told me himself... that he wanted to help his friend that drowned in the pool.
If Childs is threatening you, Peter wants to help his friends in any way he can.
Fix his BP, that should help his mental status.
A man should help his friends.