It is narrated from Ibn Abi Hathmah (may Allah be pleased with him) that he (peace and blessings be upon him) said: "Do not teach Quraysh, but learn from them; do not go ahead of Quraysh, nor lag behind them, for one man of Quraysh has the understanding of two men."
This is mursal (with the Companion missing from the chain); it has also been narrated with a connected chain, but that is not strong.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5297