Whenever the Messenger of Allah ﷺ performed bowing, he would spread his fingers apart, and whenever he performed prostration, he would keep his fingers together.
كان رسول الله ﷺ إذا ركع فرج أصابعه، وإذا سجد ضم أصابعه.
Ibn Khuzayma (594), Ibn Hibban (1920), Hakim (1/227), and Bayhaqi (2/112) all narrated it from the hadith of Harith bin Abdullah bin Ismail bin Uqba bin Khazin, who said, Hushaym narrated to us, from Asim bin Kulayb, from Alqama bin Waail bin Hujr, from his father, and he related the hadith.Its isnad is hasan because of Ibn Khazin, for his hadith is hasan. Ibn Hibban mentioned him in Thiqat and said, "His narration is sound." Dhahabi said in Mizan, "Truthful."As for Hakim's statement, "Sahih according to the criterion of Muslim," this is a mistake on his part, for this Ibn Khazin is not among the narrators of Tahdhib at all. However, Hakim narrated it (1/224) via another route, from Amr bin Awn, who said, Hushaym narrated to us with his isnad, and he said, "According to the criterion of Muslim," and it is as he said.