ENOfficial
He said: If anyone raises and lowers his head before the imam, his forelock is in the devil’s hand. Malik transmitted it.
Source: sunnah.com
Other translations
Arabic
وَعنهُ قَالَ: الَّذِي يَرْفَعُ رَأْسَهُ وَيَخْفِضُهُ قَبْلَ الْإِمَامِ فَإِنَّمَا ناصيته بيد الشَّيْطَان ". رَوَاهُ مَالك
sunnah.com