Sayyiduna Jabir bin Abdullah (may Allah be pleased with them both) said that the Messenger of Allah (peace and blessings be upon him) said: "Today a righteous servant, Ashamah, has died, who was a most excellent man; so stand up and pray the funeral prayer over him." Then he (peace and blessings be upon him) stood up and led us, and we prayed the funeral prayer over him.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 6901
It is narrated from Sayyiduna Jabir (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) prayed the funeral prayer over the Negus, and I was in the second or third row.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 6902
Abdullah bin Yazid (may Allah be pleased with him) said that he (peace and blessings be upon him) said: "There is no deceased person over whom a group of Muslims pray the funeral prayer, their number reaching a hundred, all of them interceding for him, except that their intercession for him is accepted."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 6903
Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) said: I heard the Prophet (peace and blessings be upon him) say: "When a Muslim dies and forty men who do not associate anything with Allah attend his funeral (prayer), their intercession for him is accepted."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 6904
Malik bin Hubayrah (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) said: "When those standing in three rows of Muslims pray the funeral prayer over a Muslim and seek forgiveness for him, Paradise becomes binding for him."
So whenever Malik prayed over a funeral and found its attendees few, he would arrange them into three rows and then pray over it. In the narration of Yazid bin Harun: "except that he is forgiven."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 6905