Sayyiduna Zubayr (may Allah be pleased with him) narrates: I saw the Prophet (peace and blessings be upon him) in prostration. Meanwhile Sayyiduna Hasan bin Ali (may Allah be pleased with them both) came and climbed onto his back. The Prophet (peace and blessings be upon him) did not put him down until he himself came down. The Prophet (peace and blessings be upon him) would spread his legs apart for him, and he would go in from one side and come out from the other side.
Tabarani recorded it; its chain contains Ali bin Abis, who is da'if (weak).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب المناقب / 15034