Sayyiduna Sa’d bin Abi Waqqas (may Allah be pleased with him) stated in his final will that when I die, make my grave in the form of a lahd, and do it in the same way as was done with the Prophet (peace and blessings of Allah be upon him).
Hadith Referenceمسند احمد / مسند باقي العشرة المبشرين بالجنة / 1601