Silsilat al-Ahadith al-Sahihah

Abdah bin Abu Lubabah narrates from Mujahid, and he from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them), that the Messenger of Allah (peace and blessings be upon him) said: "When a Muslim meets his brother and shakes hands with him by holding his hand, then sins fall from between their fingers just as leaves fall from trees in the winter season." Abdah says: I said to Mujahid: This act is very small (and the reward is so great). Mujahid said: Do not say so, because Allah Almighty has stated in His Book: O Prophet! If you were to spend all that is in the earth, you could not have joined their hearts together. But Allah has joined their hearts together. Abdah says: From this, I recognized Mujahid’s superiority over the other (scholars).