Is there any other proof for rewards being multiplied by seventy on Fridays?
I could not locate an authentic narration that states so.
Imam Razin (rahimahullah) has cited a narration of this meaning, but the chain first needs to be located before commenting.
(Jami’ul Usul, Hadith: 6867. Also see: Shaykh ‘Awwamah’s footnotes on Tadribur Rawi, vol.2 pg.417)
However, the day of Friday is also called: ‘Yawmul Mazid’; the day of extras/increases.
(Refer: Zadul Ma’ad, vol.1 pg.397 & Fathul Bari, before Hadith: 876)
Although it refers to the extra bounties that will be received on Fridays in jannah, this could support the expectation of general increase in rewards for good done in this world on Fridays, without specifying seventy.
And Allah Ta’ala Knows best,
Answered by: Moulana Muhammad Abasoomar