Musannaf Ibn Abi Shayba 33:225

'Abdullah ibn Idris narrated to us, from Muhammad ibn 'Ajlan, from Ibrahim, from Muhammad ibn Shihab, who said: 'Umar said: "Do not involve yourself in what does not concern you, and keep away from your enemy, and be cautious of your friend, except for the trustworthy one; for the trustworthy one among the people is not equaled by anything. And do not accompany the wicked person, for he will teach you of his wickedness, and do not disclose your secret to him, and consult in your affairs those who fear Allah."