Ikrimah narrates from Ibn Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "Some poetry is full of wisdom. When something of the Qur'an becomes confusing to you, look for it in poetry, for it is Arabic."
The first wording has also been narrated from Simak by narrators other than Isra'il; as for the second wording, it may be a statement of Ibn Abbas that has been inserted (mudraj) into the hadith.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشهادات / 21125