Qur'ān 7:21 · Al-A'raf (الأعراف)

وَقَاسَمَهُمَآ إِنِّى لَكُمَا لَمِنَ ٱلنَّـٰصِحِينَ

And he swore [by Allah] to them, "Indeed, I am to you from among the sincere advisors."