Musannaf Ibn Abi Shayba 3:2263

Hushaym narrated to us, he said: 'Awf informed us, from al-Hasan, that he did not see any harm in a man praying while he is in the *ihtiba* position (sitting with his knees drawn up to his chest and held by his arms or a garment). And Ibn Sirin used to dislike it.