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.
Intercession belongs exclusively to Allaah, The Exalted (i.e. He has the sole right to grant intercession to whomever He wishes); He says (what means): {Say, "To Allaah belongs (the right to allow) intercession entirely. To Him belongs the dominion of the heavens and the earth. Then to Him you will be returned."} [Quran 39:44] None shall be granted the intercession on the Day of Judgment unless two conditions are met: the permission of Allaah is granted to the intercessor; and He (Allaah The Almighty) is pleased with the beneficiary of the intercession. Allaah, The Exalted, says (what means): {And how many angels there are in the heavens whose intercession will not avail at all except (only) after Allaah has permitted [it] to whom He wills and approves.} [Quran 53:26] Allaah, The Exalted, also says (what means): {...Who is it that can intercede with Him except by His permission?} [Quran 2:255] So, if even the angels, the Prophets of Allaah, and the pious are not to intercede with Allaah, The Exalted, for anyone (on the day of Judgment) except with His permission, then none should ask any of them in the worldly life to intercede with Allaah for him because one cannot give what he does not possess.
None of the Companions were reported to have asked the Prophet, sallallaahu ‘alayhi wa sallam, to intercede with Allaah for him on the Day of Judgment despite knowing that he, sallallaahu ‘alayhi wa sallam, shall be granted the permission to intercede with Allaah for his followers on the Day of Judgment. Verily, if such an act contained any good, then they would have hastened to do it; it is recommended for Muslims to follow in the footsteps of the early Muslim generations.
Moreover, how can one be certain that any given person who participated in jihaad (striving in the Cause of Allaah) shall be admitted to Paradise for sure? People set out for jihaad with different intentions. Abu Moosa reported that, "A bedouin asked the Prophet 'A man may fight for the sake of booty, and another may fight so that he may be mentioned by the people, and a third may fight to show his position (i.e. bravery); which of these is regarded as fighting in the Cause of Allaah?' The Prophet, sallallaahu ‘alayhi wa sallam, said, 'He who fights so that the Word of Allaah would be superior fights for the Cause of Allaah.'" [Al-Bukhari and Muslim]
In any case, asking for intercession is not shirk. Shaykhul-Islaam Ibn Taymiyyah asserted, "One's asking for the intercession of a person who is unable to intercede with Allaah for him (on the Day of judgment) is nonsense. Asking for the intercession of a living person who is absent is related to the second case, which is asking for the intercession of a dead person..."
Shaykh Ibn Baaz wrote, "It is permissible to ask for the intercession of the Prophet, sallallaahu ‘alayhi wa sallam, in his lifetime and on the Day of Judgment because he, sallallaahu ‘alayhi wa sallam, is able to intercede with Allaah; he, sallallaahu ‘alayhi wa sallam, can implore Allaah and intercede with Him for someone. As for asking for someone’s intercession in the worldly life, this is not exclusive to the Prophet, sallallaahu ‘alayhi wa sallam, as one may ask for the intercession of any of his Muslim brothers. It is permissible for the Muslim to ask his brother saying, 'Intercede with Allaah for me regarding such-and-such,' meaning, 'Supplicate Allaah for me regarding such-and-such.' It is permissible for the Muslim to respond to such a request and implore Allaah for the sake of such a person in whatever is deemed permissible for the Muslim to ask for. As for the Day of Judgment, none has the right to intercession except those whom Allaah shall grant permission; Allaah, The Exalted, says (what means): {... Who is it that can intercede with Him except by His permission?} [Quran 2:255]"
Allaah Knows best.