It is narrated from Urwah bin al-Zubayr (may Allah have mercy on him), in mursal form: "On the night of the Battle of the Confederates (al-Ahzab), the Prophet (peace and blessings be upon him) sent Sayyiduna al-Zubayr (may Allah be pleased with him) and another man out on a moonlit night (to spy on the enemy). The two of them went, observed the situation and then came back. At that time the Messenger of Allah (peace and blessings be upon him) was wrapped in a woollen sheet (mirt) belonging to Sayyidah Umm Salamah (may Allah be pleased with her), and he (peace and blessings be upon him) took the two of them in with him under that same sheet, while the Messenger of Allah (peace and blessings be upon him) was close against the side of Sayyidah Umm Salamah (may Allah be pleased with her)."
I (Ibn Hajar) say: This narration is mursal but its chain is sahih (authentic), and there is (in some respects) reservation or criticism about it.
Hadith Referenceالمطالب العالية بزوائد المسانيد الثمانية / كتاب السيرة والمغازي / 4277
Hadith Gradingمحدثین:إسناده صحيح، مرسل
Hadith Takhrij«حکم الحدیث المطالب العالیہ محققاً تنسیق د. سعد بن ناصر بن عبد العزيز الشَّثري- مکتبہ شاملہ :قال ابن حجر: هَذَا مُرْسَلٌ صَحِيحُ السَّنَدِ ، ذُكِرَ فِيهِ نَظَرٌ . » «انفرد به المصنف من هذا الطريق»