Humayd bin Hilal (may Allah have mercy on him) said: A freed slave of Sayyiduna Abu Mas'ud (may Allah be pleased with him) narrated to me that Abu Mas'ud (may Allah be pleased with him) came to Sayyiduna Hudhayfah (may Allah be pleased with him) and said: "Give me your counsel." He said: "Has certainty not come to you?" He said: "Indeed it has, by the might of my Lord!" He said: "The true misguidance is that you come to approve what you (formerly) rejected, and to reject what you (formerly) approved. And beware of wavering between views, for the religion of Allah is one."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 19896