Some blogs on internet claim that,
During Samudra Manthanam, Halahaal the fuming posion capable of burning universe appeared and all Dev Danav Manav Yaksha Gandharva fled. All of them along with Lord Vishnu and Lord Bramha came to Lord Shiva. Lord Shiva consumed Halahaal and held it in his throat. However unable to bear its consequences it started burning him. The Vish purush sprung out of Him. Lord Shiva told him, " Although we (lord Vishnu and Lord Shiva) didn’t let you kill the people, yet in Dwapar Yuga during Mahabharat war with my blessings you will be able to kill oppressive kshatriyas. Later you will assume the post of Saptarishis in following Manvantara. You will be born as Bhardwaja’s grandson and be raised as Brahman but attracted towards Kshatriyahood ".
Which Scriptures describe springing out "Vish Purusha" from throat of Lord Rudra aka Shiva? Are there any scriptures which prophesied the birth of Aswatthama other than Mahabhartha?