On Infinity by Euler

We may here deduce from it a few consequences that are extremely curious, and worthy of attention. The fraction $\frac{1}{\infty}$ represents the quotient resulting from the division of the dividend 1 by the divisor $\infty$. Now, we know, that if we divide the dividend 1 by the quotient $\frac{1}{\infty}$, which is equal to nothing, we obtain again the divisor $\infty$ : hence, we acquire a new idea of infinity ; and learn that it arises from the division of 1 by 0 ; so that we are thence authorised in saying, that 1 divided by 0 expresses a number infinitely great, or $\infty$.

Euler, Elements of Algebra