Muwatta Imam Malik Book of Burials, Hadith 57
Malik related to me from AIqama ibn Abi Alqama that his mother said that she had heard A'isha, the wife of the Prophet ﷺ say, "The Messenger of Allah ﷺ rose one night and put on his clothes and then went out. I ordered my slave-girl, Barira, to follow him, and she followed him until he got to al-Baqi. He stood near it as long as Allah willed and then he left. Barira arrived back before him and told me and I did not say anything to him until morning, and then I mentioned it to him and he explained, 'I was sent out to the people of al-Baqi to pray for them.' "
وَحَدَّثَنِي مَالِكٌ، عَنْ عَلْقَمَةَ بْنِ أَبِي عَلْقَمَةَ، عَنْ أُمِّهِ، أَنَّهَا قَالَتْ سَمِعْتُ عَائِشَةَ، زَوْجَ النَّبِيِّ ﷺ تَقُولُ : قَامَ رَسُولُ اللَّهِ ﷺ ذَاتَ لَيْلَةٍ فَلَبِسَ ثِيَابَهُ ثُمَّ خَرَجَ - قَالَتْ - فَأَمَرْتُ جَارِيَتِي بَرِيرَةَ تَتْبَعُهُ، فَتَبِعَتْهُ حَتَّى جَاءَ الْبَقِيعَ، فَوَقَفَ فِي أَدْنَاهُ مَا شَاءَ اللَّهُ أَنْ يَقِفَ، ثُمَّ انْصَرَفَ فَسَبَقَتْهُ بَرِيرَةُ فَأَخْبَرَتْنِي، فَلَمْ أَذْكُرْ لَهُ شَيْئًا حَتَّى أَصْبَحَ ثُمَّ ذَكَرْتُ ذَلِكَ لَهُ فَقَالَ : " إِنِّي بُعِثْتُ إِلَى أَهْلِ الْبَقِيعِ لأُصَلِّيَ عَلَيْهِمْ " .