Al-Bayhaqi reported: Ahmad ibn Hanbal, may Allah be pleased with him, would supplicate in prostration, “O Allah, whomever among this nation is not upon the truth, but thinks he is upon the truth, bring him back to the truth that he may be among the people of truth.” And he would say, “O Allah, if you accept a ransom from the sinful among the nation of Muhammad, peace and blessings be upon him, then make me their ransom.”
Source: al-Bidāyah wal-Nihāyah 14/390
عن الْبَيْهَقِيُّ عَنْ أ أَحْمَدَ بن حنبل رضي الله عنه وَكَانَ دُعَاؤُهُ فِي السُّجُودِ اللَّهُمَّ مَنْ كَانَ مِنْ هَذِهِ الْأُمَّةِ عَلَى غَيْرِ الْحَقِّ وَهُوَ يَظُنُّ أَنَّهُ عَلَى الْحَقِّ فَرُدَّهُ إِلَى الْحَقِّ لِيَكُونَ مِنْ أَهْلِ الْحَقِّ وَكَانَ يَقُولُ اللَّهُمَّ إِنْ قَبِلْتَ مِنْ عُصَاةِ أُمَّةِ مُحَمَّدٍ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فِدَاءً فَاجْعَلْنِي فِدَاءً لَهُمْ
14/390 البداية والنهاية