Authentic
Sahih Muslim 954a
The Prophet (may Allah's peace and blessings be upon him) prayed over a grave after he had been buried, making four Takbīrs
Ibn ‘Abbās (may Allah be pleased with him) reported: The Prophet (may Allah's peace and blessings be upon him) prayed over a grave after he had been buried, making four Takbīrs.
صَلَّى عَلَى قَبْرٍ بَعْدَ مَا دُفِنَ فَكَبَّرَ عَلَيْهِ أَرْبَعًا .