Musnad Ahmad 1153:201

Isma'il narrated to us, he said: Ayyub informed us, from 'Abdullah ibn Abi Mulaykah, from 'Aishah, she said: The Messenger of Allah (peace and blessings of Allah be upon him) recited: "It is He who has sent down to you, [O Muhammad], the Book; in it are verses [that are] precise - they are the foundation of the Book - and others unspecific. As for those in whose hearts is deviation [from truth], they will follow that of it which is unspecific, seeking discord and seeking an interpretation [suitable to them]. And no one knows its [true] interpretation except Allah. But those firm in knowledge say, 'We believe in it. All [of it] is from our Lord.' And no one will be reminded except those of understanding." Then he said: "If you see those who argue about it, they are the ones whom Allah (Mighty and Majestic is He) meant, so beware of them."