It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) and Sayyidah Aisha (may Allah be pleased with her) that the blessed grave of the Noble Prophet (peace and blessings be upon him) was made with a side niche.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 4762
Hadith Gradingحکم دارالسلام:صحيح لغيره، وهذا إسنادان ضعيفان لضعف العمري