Shiva Purana
असाधारणकर्मा च सृष्ट्यादिकरणात्पृथक् ॥ ब्रह्मणोपि शिरश्छेत्ता जनकस्तस्य तत्सुतः ॥ १२१ ॥
He is also an extraordinary worker, separate from the creation and other activities. Janaka, his son, cut off the head of Brahma as well.
english translation
asAdhAraNakarmA ca sRSTyAdikaraNAtpRthak ॥ brahmaNopi zirazchettA janakastasya tatsutaH ॥ 121 ॥
hk transliteration by Sanscript