Ikrimah (may Allah have mercy on him) narrates from Ibn Abbas (may Allah be pleased with them both): When you recite the Qur'an and cannot find out its explanation, then look for it in poetry, for it is the literature of the Arabs.
This is the correct version: mawquf (a statement of the Companion).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشهادات / 21124