Is it permissible for a Sunni Muslim to supplicate with Shiite supplications, such as Ziyarat 'Ashura, and to seek consultation and intercession [through them]? And are there alternative supplications?

Supplication (Du'a) holds great significance in repelling afflictions. The best supplications are those authentically narrated from the Qur'an and Sunnah, such as the supplication of Yunus (peace be upon him): (There is no deity except You; exalted are You. Indeed, I have been of the wrongdoers), and the supplication for worry and grief: "O Allah, indeed I am Your servant...", and the supplication of the Prophet (peace and blessings of Allah be upon him): "O Allah, I seek refuge in You from worry and grief...". One must avoid innovative supplications (bid'i du'as) like the "Yastashir" supplication and the "Tawassul" (seeking intercession) that involves polytheism (shirk) with Allah. One should adhere to the manners and causes for acceptance of supplication, such as supplicating between the adhan and iqamah, and in the last third of the night, and beginning with praising Allah and sending blessings upon the Prophet (peace and blessings of Allah be upon him), and asking Him by His Greatest Name. If mediation by a righteous person between the spouses is possible, then let it be done.