Sayyidah Safiyyah (may Allah be pleased with her) narrates that she came to the Prophet (peace and blessings be upon him) to visit him in his i'tikaf, which he (peace and blessings be upon him) was observing in the mosque during the last ten days of Ramadan. She talked with him (peace and blessings be upon him) for a while, then got up to leave, and the Prophet (peace and blessings be upon him) also got up to see her off, until he (peace and blessings be upon him) came to the door of the mosque which was beside the door of Umm Salamah (may Allah be pleased with her). Two Companions from the Ansar (may Allah be pleased with them both) passed by there; they greeted the Prophet (peace and blessings be upon him) with salam and walked on. The Messenger of Allah (peace and blessings be upon him) said: "Stay where you are; this was Safiyyah bint Huyayy." They both said: "Subhan Allah (Glory be to Allah)!" O Messenger of Allah (peace and blessings be upon him), what is this? This weighed heavily upon them, and the Prophet (peace and blessings be upon him) said: "Indeed, Shaytan reaches within the son of Adam as far as the blood reaches, and I feared that something might settle in your hearts."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8605