It's not taxable income.
since this is a partnership the book entry could be a debit to cash and a credit to the partner's capital account (capital contribution during the year for schedule L of the partner's k-1) and for the 1065 schedule M-2 line 2a.
when repaid it would be a credit to cash and would show up on the partners k-1 as a withdrawal on schedule L of the k-1 and also line 19a of the k-1 - cash distributions. it would also appear on the 1065 M-2 line 6a.
This is a common occurrence.
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the other option, not recommended, is to treat it as a loan from partner in which case it would not be reported on the partner's k-1 and would not show up in the M-2. instead it would show on line 19a of schedule L unless repaid before year-end. partner loans can create a tax issue depending on the amount because of the various tax rules concerning loans included imputed interest rules.
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paying business expenses from a personal account is the worst option, because this can cause tax issues if there's an audit.
