I heard something which I did not know before and would be thankful if you can enlighten me. My question is did any Sahaba of Rasulallah (saw) drink his blood, for example when he was injured during the Uhud war or when he was being treated by way of cupping?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

It is reported that some Companions drank the blood of the Prophet, sallallaahu ‘alayhi wa sallam, like ‘Abdullaah ibn Az-Zubayr when he was young. It is reported from ‘Aamir ibn ‘Abdullaah ibn Az-Zubayr that he said, “I heard my father saying that he went to the Messenger of Allaah, sallallaahu ‘alayhi wa sallam, while he was being cupped. When he finished he said: “O ‘Abdullaah! Take this blood and spill it where no one can see you.” When he disappeared from the sight of the Messenger of Allaah, sallallaahu ‘alayhi wa sallam, he took the blood and drank it. When he returned, he, sallallaahu ‘alayhi wa sallam, asked him: “What have you done with the blood?” He said, “I put it in the most hidden place I know of.” He, sallallaahu ‘alayhi wa sallam, said: “Perhaps you have drunk it.” He answered in the affirmative, thereupon he, sallallaahu ‘alayhi wa sallam, said: “Why have you drunk it? Woe to the people from you, and woe to you from the people!” This story is reported by Ad-Daaraqutni, Al-Haakim and Al-Bazzaar all.

Another Companion who did that is Maalik ibn Sinaan : When the Messenger of Allaah, sallallaahu ‘alayhi wa sallam, was injured on the day of the Battle of 'Uhud, Maalik ibn Sinaan sucked his wound until he cleansed it and it looked white. He was told to spit it out, and he said, “No, by Allaah, I will never spit it out!” Then, he turned back and went on fighting. Upon that the Prophet, sallallaahu ‘alayhi wa sallam, said: “He, who likes to see a man from the inhabitants of Paradise, let him look at this man (Maalik ibn Sinaan).” He then fell as a martyr. Al-Haafith Ibn Hajar said, “Sa‘eed ibn Mansoor narrated this Hadeeth through a Mursal chain of narrators (i.e. the source of this Hadeeth is a Taabi’i [a successor of the Prophet’s Companions]).”

Also, among those (who are reported to have drunk the blood of the Prophet, sallallaahu ‘alayhi wa sallam) is Saalim Abu Hind, the cupper of the Prophet, sallallaahu ‘alayhi wa sallam. It is reported by Abu Nu‘aym in “Ma‘rifat As-Sahaabah” that he (Saalim Abu Hind) said, “I cupped the Messenger of Allaah, sallallaahu ‘alayhi wa sallam, and when I finished I drank the blood. I said: “O Messenger of Allaah! I have drunk it.” He, sallallaahu ‘alayhi wa sallam, said: “Allaah's mercy be upon you O Saalim! Do you not know that drinking blood is unlawful? Do not do it again.” According to Al-Haafith, its chain of narrators includes Abu Al-Hajjaaf, who is the subject of dispute (among the scholars of Hadeeth).

Furthermore, Safeenah, the freed slave of the Messenger of Allaah, sallallaahu ‘alayhi wa sallam, did the same. It is reported by Al-Bazzaar, Ibn Abu Khaythamah and Al-Bayhaqi in his Shu‘ab and Sunan on the authority of Safeenah that once, the Messenger of Allaah, sallallaahu ‘alayhi wa sallam, had himself cupped and said to him: “Take that blood and bury it far from animals, birds and people.” He said, “I then went far from his eyes with it and drank it. Then, when he asked me, or when I told him, he smiled.”

Allaah Knows best.