Silsilat al-Ahadith al-Sahihah

Sayyiduna Abu Rimthah (may Allah be pleased with him) says: I came to the Prophet (peace and blessings of Allah be upon him) with my father. The Prophet (peace and blessings of Allah be upon him) asked my father: "Who is this with you?" He said: "This is my son, I can testify to that." The Prophet (peace and blessings of Allah be upon him) said: "Be aware! You cannot testify falsely against him, nor can he testify falsely against you."