Yes you can use "by" two times in a sentence if needed.
If sentence is
1. I learn this poem by heart. (Active Voice)
1. This poem is learnt by me by heart (Passive Voice)

Another example could be:

I will submit the documents by tomorrow. (Active Voice)
The documents will be submitted by me by tomorrow. (Passive Voice)

I hope this would help

Regards

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I hope our Wisdom will grow with our power, and teach us, that the less we use our power the greater it will be..