Which limb should touch the ground first when going into sujud?

Hazrat Abu Huraira narrates that the Noble Prophet (peace and blessings be upon him) said: When any of you performs prostration, he should place his knees on the ground before his hands, and he should not sit in the manner of a camel.

Ibrahim narrates that Hazrat Umar used to place his knees on the ground before his hands.

Hazrat Aswad narrates that Hazrat Umar used to place his knees first.

Hazrat Nafi' narrates that Hazrat Ibn Umar (may Allah be pleased with them) used to place his knees on the ground before his hands when going into prostration, and when rising, he would lift his hands before his knees.

Hazrat Abdullah bin Muslim bin Yasar narrates from his father that when he performed sajdah, he would place his knees first, then his hands, and then his head.

Ibrahim was asked about the person who places his hands before his knees. He disliked it and also said that only a madman would do such a thing.

Hazrat Khalid says that I saw Abu Qilabah, when he performed sajdah, he would place his knees first, and when he stood up, he would support himself with his hands. And I saw Hasan, that he would bow down and then, when rising, he would stand up by supporting himself with his hands.

Hazrat Mahdi bin Maimoon says that I saw Hazrat Ibn Sirin would place his knees on the ground before his hands.

Hazrat Muammar says that Hazrat Qatadah was asked: If a person, while going from bowing (ruku) to prostration (sajdah), places his hands on the ground first, what is the ruling? He replied: One should do whichever action is easier.

Hazrat Abu Ishaq says that when the students of Hazrat Abdullah would go into prostration, they would place their knees before their hands.