First: Tabarruk is sought only for some limited, worldly benefit, whereas tawassul may be sought for any benefit, whether worldly or pertaining to the Hereafter.
Second: Tabarruk, as already explained, aims at an immediate, tangible gain, while tawassul is inseparable from supplication and is employed only in that context.
To clarify, the Law permits a Muslim, when praying, to make tawassul by mentioning one of Allah’s most beautiful names and to seek through it whatever he wishes—be it a worldly need, such as expanded provision, or an other-worldly one, such as deliverance from the Fire. He might say, for instance, “O Allah, I ask You and seek nearness to You by the fact that You are Allah, the One, the Eternal Refuge; grant me healing or admit me into Paradise ….” No one can censure him for that.
What he may not do, however, is treat a prophetic relic in the same way when practicing tabarruk. He cannot, and is not allowed to say, “O Allah, I ask You and seek nearness to You through the garment of Your Prophet—or through his saliva or his urine—that You forgive me and have mercy on me.” Whoever attempts such a thing will, without doubt, make people question his sanity and understanding, let alone his creed and religion.
Yet the plain thrust of the doctor’s words is that he allows this bizarre form of tawassul and regards it as identical to seeking blessing from one of the Prophet’s relics. By doing so he perpetrates a crude confusion, all the while showing no embarrassment in accusing the Salafis of a bewildering and baseless conflation. The readers now know who it is that really muddles the issues and thrashes about blindly.
This truly calls to mind the Arabic proverb, “She flung her own ailment at me and slipped away,” and how true are the words of the noble Prophet ﷺ: “Among the sayings that people have retained from the first prophecy is….”