Majma al-Zawaid — Hadith 5017

Sayyiduna Abu Dharr al-Ghifari (may Allah be pleased with him) narrates: I said to the Prophet (peace and blessings be upon him): "I would like to spend tonight with you and pray following your prayer." The Prophet (peace and blessings be upon him) said: "You will not be able to." Then the Prophet (peace and blessings be upon him) got up and performed the ritual bath (ghusl). A screen was made for him with a cloth, and I turned my face away from him while he bathed. Then I did the same. Then the Prophet (peace and blessings be upon him) stood up to pray, and I stood with him, until, because of the length of his prayer, I began striking my head against the wall. Then Sayyiduna Bilal (may Allah be pleased with him) came to call him to the prayer. The Prophet (peace and blessings be upon him) asked: "Have you done it?" He said: "Yes." The Prophet (peace and blessings be upon him) said: "O Bilal! You give the call to prayer (adhan) when the dawn is still spread lengthwise up the sky, and that is not the true dawn; the true dawn spreads like this, across the breadth (of the horizon)." Then the Prophet (peace and blessings be upon him) called for his pre-dawn meal and ate suhur.
Ahmad recorded it, and its chain contains a narrator, Rishdin bin Sa'd, about whom there has been much criticism, though he has also been declared trustworthy.