The parable of the righteous companion

It is narrated from Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) that he said: "The example of a good and righteous companion is like that of the one who has musk (a perfume seller): even if he gives you none of it, its fragrance will certainly reach you. And the example of a bad companion is like that of the one who blows the furnace (a blacksmith): even if he does not burn your clothes, its smell will reach you, or its foul stench will affect you."
The chain of this report has a supporting narration (shahid) in the Sahihayn, from the hadith of Sayyiduna Abu Musa al-Ash'ari (may Allah be pleased with him).

It is narrated from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) was asked: "O Messenger of Allah, which of our companions is the best?" He (peace and blessings be upon him) said: "The one whose sight reminds you of Allah, whose speech increases your good deeds, and whose conduct reminds you of the Hereafter."
Abu Ya'la also narrated this same text with his chain, through Abdullah bin Muhammad bin Aban, Ali bin Hashim and Mubarak bin Hassan.