Let $p$ be a prime $\ne 2,5$
Prove $\exists i\le 9$ such that $(\frac{i}{p})=(\frac{i+1}{p})=1$ where $(.)$ is the Legendre symbol.
I tried to use the Euler formula $(\frac{a}{p})\equiv a^{\frac{p-1}{2}} \mod p$ but it leads nowhere.
Thank you for any hints.
Edit
We should also have $p\ne 3$ for the statement above to be correct as 2 is not a quadratic residue modulo $3$.
Note: I assume you intend $i\in \{1,2,\cdots, 9\}$, else $i=0$ is a cheap example.
Hint: argue that at least one of $2,5,10$ is a quadratic residue $\pmod p$.