The translation of the Qur'an by Maulana Wahiduddin Khan contains:
God does not wrong anyone by as much as a grains weight. If there be a good deed, He will repay twofold, and will bestow out of His own bounty an immense reward. -- Qur'an 4:40 (translation available from Islam Awakened)
I'm skeptical at the word "twofold" here in particular, and I see that other translations do not use that word. I want to check if this specific numerical increase (a factor of two) in good deeds is supported (or even partially implied) by the Arabic text.
Question: Is the translation of Qur'an 4:40 "If there be a good deed, He will repay twofold" inaccurate?
Tafsir suggest it's a "doubling", but it's still not clear:
(He will double it) from one to ten times (and will give (the doer) from His presence an immense reward) an abundant reward in Paradise. -- Tanwîr al-Miqbâs min Tafsîr Ibn ‘Abbâs
...and if it be a good deed, He will double it, and it cannot be a good deed unless it is [done] for Him -- Kashani Tafsir
...if it be a good deed, He will double it and give from Himself a great wage. -- Al Qushairi Tafsir